Burr hole cap assembly with therapy delivery member orientation feature

ABSTRACT

In some examples, a burr hole cap assembly includes one or more markers that indicate a rotational orientation of a therapy delivery member relative to the burr hole cap assembly, where the therapy delivery member extends through an opening defined by the burr hole cap assembly. In addition, in some examples, the burr hole cap assembly includes a feature that indicates the rotational orientation of the therapy delivery member after the therapy delivery member is implanted in the patient. The feature can include the one or more markers in some examples.

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/480,851 by Goetz et al., which was filed on Apr.29, 2011, and is entitled “BURR HOLE CAP ASSEMBLY WITH THERAPY DELIVERYMEMBER ORIENTATION FEATURE.” U.S. Provisional Application Ser. No.61/480,851 by Goetz et al. is incorporated herein by reference in itsentirety

TECHNICAL FIELD

The disclosure relates to burr e cap assemblies.

BACKGROUND

In some medical systems, a therapy delivery member (e.g., a lead or acatheter) is implanted in a brain of a patient. The therapy deliverymember may access regions of the brain through a burr hole formedthrough the patient's skull. A burr hole cap assembly, which ispositioned within the burr hole, may be used to retain the position ofthe therapy delivery member relative to the burr hole, as well assubstantially plug the burr hole.

SUMMARY

In general, the disclosure is directed to a burr hole cap assembly thatindicates a rotational orientation of a therapy delivery member relativeto the burr hole cap assembly, where the therapy delivery member extendsthrough a base of the burr hole cap assembly. The burr hole cap assemblyincludes one or more features that indicate the rotational orientationof the therapy delivery member relative to the burr hole cap assembly.In some examples, the feature is a marker that indicates the rotationalorientation of the therapy delivery member. In some examples, the markeris visible by the clinician, without the use of any additionalvisualization tools (e.g., a medical imaging device), at the time thetherapy delivery member is implanted in the patient. In addition, insome examples, the marker is movable relative to a part of the burr holecap assembly, and a clinician may manipulate the marker at the time thetherapy delivery member is implanted in the patient so that the markerindicates the rotational orientation of the therapy delivery memberrelative to the burr hole cap assembly.

In some examples, the burr hole cap assembly includes a feature thatindicates the rotational orientation of the therapy delivery memberafter the therapy delivery member is implanted in the brain of thepatient. For example, the burr hole cap assembly may include a reactiveelement (e.g., an inductor in a circuit with a resistor and/or acapacitive element, or a capacitive element in a circuit) that has ancharacteristic (e.g., an impedance, such as an inductive reactance ofthe inductor, or a capacitance) that is indicative of the rotationalorientation of the therapy delivery member relative to the burr hole capassembly.

In one aspect, the disclosure is directed to a system comprising a basethat is configured to fit inside of a burr hole in a cranium of apatient, where the base defines an opening that is configured to receivea therapy delivery member, a marker that is configured to indicate arotational orientation of the therapy delivery member relative to thebase, and a cover that is configured to substantially cover the openingdefined by the base.

In another aspect, the disclosure is directed to a method comprisingintroducing a therapy delivery member through an opening defined by abase, where the base is configured to fit inside of a burr hole in acranium of a patient, and indicating a rotational orientation of thetherapy delivery member relative to the base with a marker.

In another aspect, the disclosure is directed to a system comprisingmeans for covering a burr hole in a cranium of a patient, wherein themeans for covering the burr hole defines an opening configured toreceive a therapy delivery member, and means for indicating a rotationalorientation of the therapy delivery member relative to the means forcovering the burr hole.

In another aspect, the disclosure is directed to a method comprisingidentifying a marker of a burr hole cap assembly, where the burr holecap assembly comprises a base that is configured to fit inside of a burrhole in a cranium of a patient, where the base defines an opening thatis configured to receive a therapy delivery member, and determining arotational orientation of a therapy delivery member relative to the basebased on a position of the marker relative to the base.

In another aspect, the disclosure is directed to a method comprisingdetermining a characteristic of a reactive element that changes based ona position of a marker of a burr hole cap assembly relative to a base ofthe burr hole cap assembly, wherein the base is configured to fit insideof a burr hole in a cranium of a patient and defines an opening that isconfigured to receive a therapy delivery member, and, with a processor,determining a rotational orientation of the therapy delivery memberrelative to the base based on the characteristic of the reactiveelement.

In another aspect, the disclosure is directed to an article ofmanufacture comprising a computer-readable storage medium. Thecomputer-readable storage medium comprises computer-readableinstructions for execution by a processor. The instructions cause aprogrammable processor to perform any part of the techniques describedherein. The instructions may be, for example, software instructions,such as those used to define a software or computer program. Thecomputer-readable medium may be a computer-readable storage medium suchas a storage device (e.g., a disk drive, or an optical drive), memory(e.g., a Flash memory, read only memory (ROM), or random access memory(RAM)) or any other type of volatile or non-volatile memory that storesinstructions (e.g., in the form of a computer program or otherexecutable) to cause a programmable processor to perform the techniquesdescribed herein. The computer-readable medium may be nontransitory.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual illustration of a therapy delivery memberimplanted in a brain of a patient through a burr hole defined through acranium of the patient.

FIG. 2 is a conceptual cross-sectional illustration of a therapydelivery member extending through a base of a burr hole cap assemblythat is inserted in a burr hole defined through a cranium of a patient.

FIGS. 3A and 3B are conceptual side views of example therapy deliverymembers, which each includes a plurality of columns of electrodes andmarkers that indicate the circumferential positions of the columns ofelectrodes.

FIG. 4 is conceptual side view of an example therapy delivery member,which includes a fluid delivery port and a marker that indicate thecircumferential position of the fluid delivery port.

FIG. 5 is a conceptual perspective view of an example burr hole capassembly that includes a plurality of markings that may indicate arotational orientation of a therapy delivery member extending throughthe burr hole cap assembly.

FIG. 6 is a conceptual top view of the example burr hole cap base ofFIG. 5 and illustrates a therapy delivery member extending through theburr hole cap assembly base.

FIG. 7 is a flow diagram illustrating an example technique fordetermining a rotational position of a therapy delivery member relativeto a burr hole cap assembly.

FIG. 8 is a conceptual illustration of another example burr hole capassembly, which includes a base and a set screw that is movable relativeto the base.

FIG. 9 is a flow diagram illustrating an example technique determining arotational position of a therapy delivery member relative to a burr holecap assembly that includes a set screw.

FIG. 10A is a conceptual perspective view of a part of another exampleburr hole cap assembly, which includes a base and a rotating membercomprising a marker.

FIG. 10B is a conceptual cross-sectional illustration of the burr holecap assembly shown in FIG. 10A.

FIG. 11 is a flow diagram of an example technique for indicating arotational position of a therapy delivery member relative to a burr holecap assembly that includes a rotatable member with a marker, where therotatable member rotates relative to a base of the burr hole capassembly that is configured to fit in a burr hole.

FIG. 12 is a conceptual top view of another example burr hole capassembly, which includes inductors, the inductive reactances of whichindicate a rotational orientation, of a.

therapy delivery member extending through an opening defined by a baseof the assembly, and a functional block diagram of a reader device.

FIGS. 13A-13C are schematic circuit diagrams of example reactiveelements that can be included in a burr hole cap assembly, where thereactive elements are each configured to indicate a rotationalorientation, of a therapy delivery member relative to the burr hole capassembly.

FIG. 14 is a flow diagram of an example technique for determining arotational orientation of a therapy delivery member relative to the burrhole cap assembly shown in FIG. 12.

DETAILED DESCRIPTION

FIG. 1 is a conceptual illustration of a part of an implanted therapysystem 10, which includes therapy delivery member 12 implanted withinpatient 14 through burr hole 16 defined through cranium 18 of patient14. Therapy system 10 further includes burr hole cap assembly 20, whichis configured to substantially fix therapy delivery member 12 in placerelative to burr hole 16 in cranium 18, as well as substantially coverburr hole 16. Securing a portion of therapy delivery member 12 thatpasses through cranium 18 may help secure a portion (e.g., a distalportion) of therapy delivery member 12 that is configured to delivertherapy to a target tissue site in the brain of patient 14. As describedin further detail below, burr hole cap assembly 20 includes one or morefeatures that indicate a rotational orientation of therapy deliverymember 12 relative to burr hole cap assembly 20.

The rotational orientation of therapy delivery member 12 relative toburr hole cap assembly 20 may be useful for various purposes, such asfor programming a medical device (implantable or external) that deliverstherapy to patient 14 via therapy delivery member 12. In addition, insome examples, the rotational orientation of therapy delivery member 12relative to burr hole cap assembly 20 may be useful for interpreting oneor more physiological signals sensed by sensing electrodes of therapydelivery member 12 because the rotational orientation of therapydelivery member 12 relative to burr hole cap assembly 20 may indicatethe orientation of the sensing electrodes relative to one or more brainstructures of patient 14 (e.g., when the orientation of burr hole capassembly 20 relative to the one or more brain structures may be known),

Therapy delivery member 12 can be any suitable medical member that isconfigured to deliver therapy to one or more target tissue sites withinpatient 14, e.g., from a medical device to the one or more target tissuesites, or to sense one or more physiological parameters of patient 14.Therapy delivery member 12 is relatively torsionally stiff, such thattherapy delivery member 12 does not significantly rotate between thepoint at which therapy delivery member 12 extends from burr hole capassembly 20 and one or more therapy delivery elements (e.g., sensingand/or stimulation electrodes, and/or one or more fluid delivery ports)of therapy delivery member 12. In this way, the rotational orientationof therapy delivery member 12 relative to burr hole cap assembly 20,determined from the portion of therapy delivery member 12 extending fromburr hole cap assembly 20, may indicate the rotational orientation ofone or more therapy delivery elements of therapy delivery member 12.

Although not shown in FIG. 1, therapy delivery member 12 may beconnected to a medical device either directly or indirectly (e.g., viaone or more extension elements). The medical device may be implanted ormay be carried external to patient 14. In some examples, therapydelivery member 12 is a medical lead that carries a set of electrodesnear a distal end, where the electrodes may be configured to deliverelectrical stimulation therapy from the medical device to tissueproximate the electrodes. Instead of or in addition to a medical lead,therapy delivery member 12 may be a catheter that defines one or moredelivery ports that may be used to deliver a therapeutic agent (e.g., apharmaceutical agent) from a medical device to one or more target tissuesites within patient 14.

In the example therapy system 10 shown in FIG. 1, therapy deliverymember 12 forms a strain relief loop in subgaleal pocket 26, which isunder the scalp of patient 14. Subgaleal pocket 26 may have any suitabledimensions, such as an approximately 50 millimeters (mm) diameter, andmay be formed using any suitable technique, such as blunt dissection. Inother examples, therapy delivery member 12 may not form a strain reliefloop or may form a strain relief loop in another suitable region inpatient 14. In the example shown in FIG. 1, therapy delivery member 12includes cap 28, which can be delivered (e.g., via tunneling throughtissue) to another region in patient 14, such as the region in which amedical device is implanted in patient 14. The medical device may beimplanted outside of cranium 18 (e.g., in a chest region of patient 14)in some examples. However, in some examples, the medical device may beimplanted in cranium 18 of patient 14, and, as a result, there may beless strain relief of therapy delivery member 12, or distance in whichtherapy delivery member 12 is tunneled to the cranially implantedmedical device compared to examples in which the medical deviceimplanted in a portion of the body of patient 14 outside the cranium118.

As noted above, knowledge of a relative rotational orientation betweentherapy delivery member 12 and one or more brain structures may beuseful for programming therapy delivery by a medical device, such as forselecting the one or more electrodes that are used to deliver electricalstimulation to patient 14 in examples in which therapy delivery member12 comprises a lead or determining the appropriate bolus size or rate ofdelivery for a therapeutic agent that may provide therapeutic resultsfor patient 114. In addition, in some examples, knowledge of therelative rotational orientation between therapy delivery member 12 andburr hole cap assembly 20 may be useful for positioning therapy deliverymember 12 in patient 14 at a desired orientation relative to one or morebrain structures. Knowledge of the relative rotational orientationbetween therapy delivery member 12 and burr hole cap assembly 20 may beparticularly useful if therapy delivery elements of therapy deliverymember 12 are symmetrical (relative to a longitudinal axis of member 12)or unsymmetrical (e.g., a catheter with more ports on one side thananother or a lead with electrodes that are designed to provide higherresolution through some angles than others).

Burr hole cap assembly 20 includes one or more features that indicatethe relative rotational orientation between therapy delivery member 12extending through burr hole 16 and burr hole cap assembly 20. Therelative rotational orientation between therapy delivery member 12 andburr hole cap assembly 2.0 may indicate, for example, the orientation ofelectrodes, a fluid delivery port, or other therapy delivery features oftherapy delivery member 12 relative to one or more brain structures ofpatient 14. The relative orientation between burr hole cap assembly 20and one or more brain structures may be known, e.g., based on thestereotactic or other surgical data used to define burr hole 16, inwhich burr hole cap assembly 20 is placed. Thus, the relativeorientation of therapy delivery member 12 relative to the one or morebrain structures can be determined based on the relative orientation oftherapy delivery member 12 and burr hole cap assembly 20.

As described in further detail below with respect to FIGS. 5-14, in someexamples, burr hole cap assembly 20 includes one or more markers thatcan be aligned with a corresponding marker on therapy delivery member12. In this way, the one or more markers of burr hole cap assembly 20may indicate the relative rotational orientation of therapy deliverymember 12. In some examples, the one or more markers are in fixedpositions relative to burr hole cap assembly 20, while in otherexamples, the one or more markers are movable relative to burr hole capassembly 20.

In some examples, the location of the one or more markers of burr holecap assembly 20 may be determined after therapy delivery member 12 isimplanted in patient 14 and, e.g., after burr hole cap assembly 20 iscovered by the patient's scalp or otherwise not readily visible by theclinician without the aid of visualization tools. For example, the oneor more markers may be radiopaque and visible via medical imaging (e.g.,x-ray or computed tomography (CT)). As another example, in addition toor instead of the radiopaque marker, in some examples, the one or moremarkers of burr hole cap assembly may protrude from cranium 18 ofpatient 14, such that a clinician may locate the markers through thepatient's skin by a clinician via palpation. In addition to or insteadof the aforementioned markers, burr hole cap assembly 20 may include areactive element (e.g., an inductor in a circuit that includes acapacitor and/or a resistor or combinations thereof) whose impedance(e.g., an inductive reactance of the inductor) changes as a function ofthe position of a marker of burr hole cap assembly 20. An externaldevice may energize the reactive element and determine the rotationalposition of the marker of burr hole cap assembly 20, and, therefore, therotational position of a marker on therapy delivery member 12, based onthe impedance of the reactive element.

With existing systems, a clinician may implant a therapy delivery memberin patient 14 through burr hole 16 and subsequently determine and recorda rotational orientation of the therapy delivery member in anidiosyncratic manner. For example, if therapy delivery member 12includes one or more segmented or partial electrodes that extend aroundless than the entire outer perimeter of element 12, the clinician maydetermine which direction (e.g., relative to an anatomical landmark) aparticular electrode was facing when therapy delivery member 12 wasimplanted in patient 14. The clinician may then manually record thisinformation in a written record or in an electronic device (e.g., amedical device programmer or another computing device). The writtenrecord or electronic device containing the orientation information mayor may not remain with patient 14, which may reduce the availability ofthe information to clinicians that treat patient 14.

Moreover, reliance on the implanting clinician to provide theinformation indicating the rotational orientation of an implantedtherapy delivery member may result in different approaches for conveyingthe information between clinicians. For example, one clinician mayindicate a therapy delivery member is oriented at 30 degrees (°)relative to a particular point on a burr hole cap assembly or ananatomical landmark, while another clinician may refer to this exactsame orientation as −30°.

In contrast to these existing systems, with therapy system 10,information indicating a relative rotational orientation of therapydelivery member 12, e.g., relative to burr hole cap assembly 20 and/orone or more brain structures, remains with patient 14, and at a knownplace, e.g., near burr hole 16, which is the point of implant of therapydelivery member 12 in patient 14. In this way, information indicative ofthe rotational orientation of the therapy delivery member relative toburr hole cap assembly 20 is built into features provided by burr holecap assembly 20. Thus, in some examples, burr hole cap assembly 20 mayrelieve the burden on a clinician to accurately communicate and/orrecord the orientation of the therapy delivery member as implanted inpatient 14, as well as communicate and record the information in amanner that is expected to be understood by other clinicians. Inaddition, burr hole cap assembly 20 may standardize how such informationis provided across multiple clinicians. Multiple clinicians using burrhole cap assembly 20 may indicate the rotational orientation of therapydelivery member 12 in a consistent way.

While a clinician can attempt to implant therapy delivery member 12 sothat it has a particular rotational orientation relative to burr holecap assembly 20, in some cases, the clinician may find this burdensomeand difficult to achieve. In some cases, burr hole cap assembly 20enables the clinician to implant therapy delivery member 12 withouttrying to maintain a specific rotational orientation between therapydelivery member 12 and burr hole cap assembly 20. This may beadvantageous because requiring changes to surgical procedures may causethe procedure to take longer. After implantation of therapy deliverymember 12 in patient 14, the clinician may determine the relativerotational orientation between therapy delivery member 12 and burr holecap assembly 20. In some cases, this may be done at the time of implant,while in other examples, this may be done some time after implant, e.g.,after burr hole cap assembly 20 is covered up with the skin of patient14.

Burr hole cap assembly 20 may provide a convenient mechanism by whichthe clinician may record information that indicates the rotationalorientation of therapy delivery member 12 relative to burr hole capassembly 20. In some examples, the clinician may determine therotational orientation of therapy delivery member 12 relative to burrhole cap assembly 20 at the time therapy delivery member 12 is implantedin patient 14, which may be the time at which information about therotational orientation is readily accessible to the clinician. Forexample, at the time therapy delivery member 12 is implanted in patient14, the clinician may visually ascertain, without the aid of any imagingdevices, the rotational orientation of therapy delivery member 12relative to burr hole cap assembly 20.

In some examples, burr hole cap assembly 20 is configured to transmitinformation indicative of the relative rotational orientation betweentherapy delivery member 12 and burr hole cap assembly 20 to an externaldevice, such as a medical device programmer or a reader device(described below with respect to FIG. 12). In addition, in someexamples, burr hole cap assembly 20 may enable a clinician to determinethe relative orientation of therapy delivery member 12 and the brainstructures of patient 14 without medical imaging. Medical imaging may beinconvenient, costly; or both, in some cases.

Even if therapy delivery member 12 includes a radiopaque marker, theradiopaque marker on member 12 by itself may not be useful fordetermining the direction the one or more therapy delivery elements oftherapy delivery member 12 face within patient 14. For example, themarker of therapy delivery member 12 may be covered by burr hole capbase 20, which may complicate the imaging of the marker. Placement of amarker on burr hole cap assembly 20 may be advantageous in that themarker may be more visible to a clinician (e.g., via medical imaging)compared to a marker on therapy delivery member 12. In addition, due tothe placement of burr hole cap assembly 20 in patient 14 versus theplacement of an implanted therapy delivery member 12 in patient 14, theradiopaque marker on burr hole cap assembly 20 may allow for a simpleror more available form of medical imaging (e,g., x-ray or fluoroscopy)to determine the location of the radiopaque marker compared to the formsof medical imaging (e.g., magnetic resonance imaging (MRI) or computedtomography imaging) that may be required to determine the location ofthe marker on therapy delivery element 12.

In addition or instead, imaging of a marker on therapy delivery member12 by itself may not be useful for determining which direction the oneor more therapy delivery elements of therapy delivery member 12 face inpatient 114. For example, an x-ray image may not provide a referencepoint for the marker of therapy delivery member 12, such that an imageof the marker itself may not provide any information regardingdirectionality of the one or more therapy delivery elements of therapydelivery member 12. On the other hand, due to the position of burr holecap assembly 20 on cranium 18 of patient 14, a reference point for animaged marker of burr hole cap assembly 20 may be automatically known.As an example, based on an image of a marker of burr hole cap assembly20, a clinician may approximate where the marker is on cranium 18, whichmay then indicate which direction the one or more therapy deliveryelements of therapy delivery member 12 are facing relative to burr holecap assembly 20.

FIG. 2 is a schematic cross-sectional illustration of therapy deliverymember 12 extending through base 22 of burr hole cap assembly 20, wherebase 22 is positioned within burr hole 16 through cranium 18 of patient14. The cross-section is taken through burr hole cap assembly 20, aswell as through a center of therapy delivery member 12. As shown in FIG.2, burr hole cap assembly 20 includes base 22, which defines opening 30,and cover 24 which is shown in FIG. 2 in a disassembled state, in whichcover 24 is not mechanically coupled to base 22. Assembly lines areshown in FIG. 2 to illustrate how cover 24 may be aligned with base 22such that it partially fits within opening 30 define by base 22 andsubstantially covers opening 30.

Opening 30 defined by base 22 is configured to receive therapy deliverymember 12. In some examples, opening 30 has a circular cross-section,but other cross-sectional shapes (e.g., quadrilateral) are contemplated.In the example shown in FIG. 2, opening 30 has a width W (e.g., widthmay be a diameter in the case of an opening with a circularcross-section), which is the width at the widest portion of opening 30.In addition, opening 30 is sized to receive therapy delivery member 12.For example, width W may be greater than a greatest dimension of therapydelivery member 12 in a direction that is substantially perpendicular toa longitudinal axis of therapy delivery member 12. For example, in FIG.2, width W of opening 30 is sized to be larger than a diameter D oftherapy delivery member 12 in examples in which therapy delivery member12 has a circular cross-section. In one example, for example, width W ofopening 30 is about 14 mm and diameter D of therapy delivery member 12is about 1.3 mm. Other dimensions are contemplated.

Base 22 is configured to be inserted in burr hole 16 and may helpprotect edges of burr hole 16. Base 22 may have any suitableconfiguration. In the example shown in FIG. 2, base 22 includes flange32 that radially extends from shaft 34. Flange 32 may be integrallyformed with shaft 34, or may be physically separate from shaft 34 andmechanically coupled to shaft 34. Flange 32 is configured to engage withcranium 18 outside of burr hole 16 and shaft 34 is configured to engagewith cranium 18 within burr hole 16. The intersection between flange 32and shaft 34 may cover the edges of burr hole 116. The extension offlange 32 in a generally radially outward direction from shaft 34 helpsto secure burr hole cap assembly 20 to an outer surface (i.e., thesurface opposite the surface closest to the brain) of cranium 18.

In some examples, base 22 and cap 24 may be configured to minimizevertical height of the structure above the outer surface of cranium 18,which may help manage, minimize, and control the reossification (bonegrowth) of the burr hole post surgically.

In the example shown in FIG. 2, base 22 is configured such that therapydelivery member 12 extends from a side of burr hole cap assembly 20,rather than from a top of burr hole cap assembly 20 (e.g., the surfacefurthest from cranium 18) when burr hole cap assembly 20 is placed inburr hole 18. In one example, flange 32 defines a plurality of grooves,including groove 33A, which is configured to receive therapy deliverymember 12. Therapy delivery member 12 may be configured to extend fromburr hole cap assembly 20 through groove 33A. Groove 33A may be, forexample, a channel configured to guide therapy delivery member 12 out ofburr hole cap assembly 20. In some examples, flange 32 of base 22defines a plurality of grooves, which may enable a clinician to selectthe point around base 22 that therapy delivery member 12 exits burr holecap assembly 20. In some examples, grooves defined by flange 32 may beradially oriented or may begin radially oriented but then curve tospiral therapy deliver element 112, allowing the lead to more graduallyenter into strain relief loops surrounding burr hole 16.

In other examples, burr hole cap assembly 20 is configured such thattherapy delivery member 12 exits burr hole cap assembly 20 from anothersurface of assembly 20, such as from a top of burr hole cap assembly 20.For example, cover 24 may define an opening that substantially alignswith opening 30 in base 22 when cover 24 is connected to base 22, andtherapy delivery member 12 may exit burr hole cap assembly 20 throughthe opening defined by cover 24. This may permit the radius of curvatureof therapy delivery element 12 as it exits burr hole cap assembly 20 tobe controlled, which may help maintain the integrity of therapy deliveryelement 12. Other techniques for guiding therapy delivery member 12 outof burr hole cap assembly 20 may be used. The techniques may beconfigured to guide therapy delivery member 12 in a manner that helpsmaintain the mechanical integrity of therapy delivery member 12.

Base 22 may be affixed to cranium 18 of patient 14 using any suitabletechnique, e.g., by suturing or via set screws. For example, base 22 maydefine apertures configured to receive one or more sutures, set screws,by mechanical interference fit, or by screwing base 22 into the burrhole itself. In some examples, at least a portion of base 22 may beformed from a compressible material, such that shaft 34 of base 22 maybe sized as needed to accommodate a predetermined range of burr holesizes. In other examples, base 22 is sized specifically for one burrhole size.

Cover 24 is configured to be mechanically connected to base 22 andsubstantially cover (e.g., plug) opening 30 defined by base 22. In thisway, cover 24 may substantially cover burr hole 16. In some examples ofburr hole cap assembly 20, cover 24 is also configured to fix therapydelivery member 12 substantially in place, e.g., in groove 33A inexamples in which base 22 defines groove 33A, thereby substantiallyretaining the relative position between therapy delivery member 12 andburr hole 16 when burr hole cap 20 is substantially fixed to cranium 18.In the example shown in FIG. 2, cover 24 is configured to cover groove33A (as well as the other grooves 33), such that when cover 24 ismechanically connected to base 22, therapy delivery element 12 extendsfrom burr hole cap assembly 20 through a relatively small openingdefined between base 22 and cover 24. In other examples, therapydelivery member 12 is fixed substantially in place by base 22, or bothbase 22 and cover 24.

In the example shown in FIG. 2, therapy delivery member 12 extendsthrough opening 30 defined by base 22 of burr hole cap assembly 20 toaccess a brain of patient 14, which is positioned on the other side ofcranium 18 from burr hole cover 24. When cover 24 is installed over base22 and cover 24 is secured to base 22 (e.g., via a snap fit, an adhesiveor any other suitable mechanically fixation), cover 24 helps retain theposition of therapy delivery member 12 relative to burr hole 16. Aspreviously discussed, this may help secure a portion (e.g., a distalportion) of therapy delivery member 12 that is configured to delivertherapy to one or more target tissue sites in the brain of patient 14.

Therapy delivery member 12 may be introduced into patient 14 using anysuitable technique. In some examples, a distal end of therapy deliverymember 12 may be guided to a target tissue site within patient 14 (e.g.,within the brain of patient 14) with the aid of a stereotacticinstrument, which may permit a very precise movement of member 12 withinpatient. In some of these examples, cover 24 is configured to fit overbase 22 while therapy delivery member 12 is stilt retained by thestereotactic instrument and held in place relative to the target tissuesite via the stereotactic instrument. Upon installation of cover 24 overbase 22, cover 24 may substantially fix therapy delivery member 12 inplace relative to burr hole 16; in examples in which therapy deliverymember 12 is relatively rigid, cover 24 may also substantially fixtherapy delivery member 12 at the target tissue site.

In other examples, cover 24 may be configured to fit over base 22 aftertherapy delivery member 12 is released from the stereotactic instrument.For example, base 22 may include one or more features that substantiallyfixes the position of therapy delivery member 12 relative to base 22prior to installation of cover 24. As an example, groove 33 may beconfigured to hold a portion of therapy delivery member 12 retained ingroove 33 by friction fit. The clinician implanting therapy deliverymember 12 in patient 14 may introduce therapy delivery member 12 intogroove 33 before or after release of therapy delivery member 12 from thestereotactic instrument (or other instrument used to implant therapydelivery member 12). Other techniques may also be used to substantiallyfix the position of therapy delivery member 12 relative to base 22 priorto installation of cover 24.

In the example shown in FIG. 2, therapy delivery member 12 comprisesmarker 36 that corresponds to a specific circumferential location, thatis in a known position relative to a therapy delivery feature (e.g., oneor more electrodes or one or more fluid delivery ports) of therapydelivery member 12. Marker 36 is in a fixed position relative to theouter perimeter of therapy delivery member 12. As described in furtherdetail with respect to FIGS. 3A-14, marker 36 is a visual aid that canbe used by a clinician to determine the relative rotational orientationbetween therapy delivery member 12 and burr hole cap assembly 20, e.g.,after therapy delivery member 12 is implanted in patient 14.

In some examples, marker 36 is visible to the human eye without the aidof additional devices. For example, marker may include any one or moreof a graphic marking on an outer surface of therapy delivery member 12,a dent in the outer surface, a tab or other structure that protrudesfrom the outer surface, and the like. In addition to being a markervisible to the human eye without the aid of additional devices, in someexamples, marker 36 is radiopaque so that it can be viewed after therapydelivery member 12 is implanted in patient 14 and burr hole 16 and burrhole cap assembly 20 is covered up by skin.

Marker 36 may have any suitable configuration. In some examples, marker36 is a stripe that is longer (where the length is measured along alongitudinal axis of therapy delivery member 12) than wide (where thewidth is measured in a direction substantially perpendicular to thelongitudinal axis of member 12). In other examples, marker 36 may becircular or have an irregular shape In the example shown in FIG. 2,marker 36 does not extend along the entire length of therapy deliverymember 12. Rather, marker 36 is positioned along a portion of therapydelivery member 12 that is expected to protrude from burr hole capassembly 20 when the one or more therapy delivery elements (e.g.,electrodes or fluid delivery portions) of member 12 are positioned atone or more target tissue sites in the brain of patient 14. In otherexamples, marker 36 extends along the entire length of therapy deliverymember 12 so that marker 36 is substantially continuously visible astherapy delivery member 12 is implanted in patient 14.

In addition, in other examples, marker 36 can be circumferentiallyaligned with one or more additional markers (not shown in FIG. 2). Forexample, marker may be positioned near a proximal end of therapydelivery member 12 while a second marker may be positioned near a distalend of therapy delivery member 12, where marker 36 and the second markermay share a circumferential position. These markers may be considered tobe axially displaced from each other (e.g., displaced along alongitudinal axis of therapy delivery member 12). An example of leadwith axially displaced, but circumferentially aligned axial markers isshown and described with respect to FIG. 3B.

While one marker 36 at one circumferential position is shown in FIG. 2,in other examples, therapy delivery member 12 may include a plurality ofmarkers that have different circumferential positions. An example of atherapy delivery member with a plurality of markers is shown in FIG. 3A.FIG. 3A is a conceptual side view of therapy delivery member 40, whichincludes a plurality of columns of electrodes 42, 44, where each column42, 44 includes a plurality of electrodes separated from each otheralong longitudinal axis 46 of therapy delivery member 40. The electrodesin each column 42, 44 substantially share a circumferential positionaround the outer circumference of therapy delivery member 40. Theelectrodes may be used to, for example, deliver electrical stimulationtherapy to tissue of patient 14 and/or sense one or more physiologicalparameters of patient 14. Therapy delivery member 40 may include anysuitable number of columns of electrodes, such as two, three, four ormore.

Therapy delivery member 40 further includes first marker 48 that isindicative of the circumferential position of one column of electrodes42 and second marker 50 that is indicative of the circumferentialposition of another column of electrodes 44. In the example shown inFIG. 3B, markers 48, 50 are circumferentially aligned with therespective column of electrodes 42, 44. In some examples, markers 48, 50are circumferentially aligned with a center line that substantiallybisects the electrodes of the respective column of electrodes 42, 44,while in other examples, markers 48, 50 are circumferentially alignedwith another part of the electrodes of the respective column ofelectrodes 42, 44, such as an edge of the electrodes.

In the example shown in FIG. 3A, markers 48, 50 extend along the entirelength of therapy delivery member 40. In other examples, as shown inFIG. 3B, markers of therapy delivery member 40 may not extend along theentire length of therapy delivery member 40. Markers of therapy deliverymembers described herein can extend along any suitable length of thetherapy delivery member up to the entire length, such as about 10% toabout 80% of the length of the therapy delivery member.

In FIG. 3B, rather than markers 48, therapy delivery member 40 includesa plurality of markers 52 that share a circumferential position aroundthe outer circumference of therapy delivery member 40, and markers 54share a circumferential position around the outer circumference oftherapy delivery member 40. Adjacent markers 52 are separated from eachother along longitudinal axis 46 of therapy delivery member 40, andadjacent markers 54 are separated from each other along longitudinalaxis 46 of therapy delivery member 40. Markers 52, 54 are positionedalong a portion of therapy delivery member 40 that may extend from burrhole 16 when columns of electrodes 42, 44 are implanted at a targetstimulation site within a brain of patient 14, and therapy deliverymember 40 extends through burr hole 16 (e.g., as shown in FIG. 2 withrespect to therapy delivery member 12).

As described above, in some examples, therapy delivery member 12 (FIGS.1 and 2) may be configured to deliver a therapeutic agent to one or moretarget tissue sites in patient 14. FIG. 4 is an example of such atherapy delivery member 60, which includes body 62 including a fluiddelivery conduit (not shown in FIG. 4) that terminates at a fluiddelivery port 64, and a marker 66 that indicates the circumferentialposition of the fluid delivery port 64. In the example shown in FIG. 4,fluid delivery port 64 is on a longitudinal surface of body 62. Marker66 may be useful for determining the rotational orientation of port 64,e.g., when port 64 is not visible to the implanting clinician. Marker iscircumferentially aligned with port 64. In some examples, marker 66 iscircumferentially aligned with a center of port 64, while in otherexamples, marker 66 is circumferentially aligned with another part ofport 64, such as an edge of port 64.

Marker 66 may have any suitable length (measured along a directionparallel to longitudinal axis 68 of body 62) that is selected toincrease the possibility that marker 66 will be visible to the clinicianwhen therapy delivery member 60 is implanted in patient 14. In theexample shown in FIG. 4, marker 66 is positioned only on a part oftherapy delivery member 60 that is expected to be visible to theimplanting clinician when therapy delivery member 60 is implanted incranium 18 (FIG. 1) of patient 14 such that therapy delivery member 60extends through burr hole 16 and fluid delivery port 66 is positioned todeliver a therapeutic agent to a target tissue site. In other examples,marker 66 can extend along the entire length of therapy delivery member60 or along a greater length of therapy delivery member than that shownin FIG. 4.

Other arrangements of markers are contemplated. In addition, if therapydelivery member 60 defines more than one fluid delivery port, therapydelivery member 60 may include additional markers that indicate thecircumferential position (e.g., are circumferentially aligned) with theone or more additional therapy delivery ports. In addition, if therapydelivery member 60 includes a plurality of fluid delivery ports, therapydelivery member 60 may include different markers for the different ports(e.g., a relatively large port being distinguished from a relativelysmall port with line thicknesses). In addition, in some examplesdescribed herein, different types of therapy delivery members(regardless of whether the member includes electrodes, fluid deliveryports, or both) may have different types of markers, such that themarkers may be used to indicate the type of therapy delivery member thatis implanted in patient 114.

FIG. 5 is a conceptual perspective view of an example burr hole capassembly 70, which is one example of burr hole cap assembly 20 (FIGS. 1and 2). Burr hole cap assembly 70 includes base 72 and cover 74, whichare similar to base 22 and cover 24 of burr hole cap assembly 20. Base72 defines opening 30 and a plurality of grooves 33A, 33B, 33C(collectively referred to as “grooves 33”), which are configured toreceive therapy delivery member 12 and through which therapy deliverymember 12 may exit burr hole cap assembly 70. Base 72 includes aplurality of markers 76 distributed around opening 30. Markers 76 are infixed positions relative to each other, as well as relative to base 72.For example, markers 76 can include lines or other graphical objectsdrawn on base 72, etched into base 72, printed onto base 72, orotherwise applied to or formed by base 72. In addition, in someexamples, markers 76 can each include a label, such as alphanumericindicators (as shown in FIG. 5), a unique color, graphical symbols, orthe like that helps distinguish one marker from another. In addition, insome examples, markers 76 may be configured to correlate to a marker ontherapy delivery element 12. For example, two or more markers 76 mayhave unique colors that match similar colored markers on therapydelivery element 12.

Markers 76 each indicate a respective location around the perimeter ofopening 30, as well as around the perimeter of base 72. In the exampleshown in FIG. 5, base 72 has a substantially circular cross-sectionalshape, and the unit of measurement of markers 76 is degrees (°), suchthat markers 76 are positioned around the 360° of a circle.

As shown in FIG. 5, in some examples, marker 76 are positioned every 15°around the perimeter of opening 30 of base 72. In other examples,markers 76 can be positioned at any suitable position and with anysuitable granularity, such as every 1° to about every 45°, such as aboutevery 35°, in some cases, the granularity provided by markers at every1° to about every 5° may not be necessary to determine the rotationalorientation of therapy delivery after therapy delivery member 12 isimplanted in patient 14.

FIG. 6 is a conceptual top view of therapy delivery member 12 introducedthrough opening 30 defined through base 72. A schematic cross-sectionalview of therapy delivery member 12 is shown in FIG, 6, as well as inFIGS, 8, 10, and 12, which are discussed below, where the cross-sectionis taken along a line substantially perpendicular to the longitudinalaxis of therapy delivery member 12. The cross-section may be taken atthe point along the length of therapy delivery member 12 that extendsfrom opening 30 defined by the base of the respective burr hole capassembly. Therapy delivery member 12 is illustrated in FIGS. 6, 8, 10,and 12 as extending substantially straight through opening 30 (e.g.,substantially parallel to a center axis of opening 30). However, in somecases, therapy delivery member 12 may be implanted at other orientationswithin opening 30 and may not extend substantially straight throughopening 30.

Base 72 may be inserted in burr hole 16 in cranium 18 (FIGS. 1 and 2) ofpatient 14, and therapy deliver member 12 may be implanted in the brainof patient 14 through base 72, and, therefore, through burr hole 16through which base 72 extends. Base 72 can be installed in burr hole 16in a known orientation (e.g., with the 0° marker 76 substantiallyaligning with a nose of a person), such that markers 76 are in knownpositions relative to burr hole 16. Because burr hole 16 is in a knownposition relative to one or more brain structures, markers 76 mayindicate the rotational orientation of therapy delivery member 12relative to burr hole cap assembly 70, from which the rotationalorientation of therapy delivery member 12 relative to one or more brainstructures of patient 14 may be determined.

Using FIG. 6 as an example, therapy delivery member 12 is implanted suchthat marker 36 on therapy delivery member 12 is substantially alignedwith the 90° marker 76 on base 72 of burr hole cap assembly 70. Asdiscussed above, marker 36 may indicate the circumferential position ofa therapy delivery element of therapy delivery member 12. Thus, themarker 76 that is substantially aligned with marker 36 after therapydelivery member 12 is implanted in patient 14 may indicate a meaningfulrotational orientation of therapy delivery member 12 in patient 14,e.g., the direction in which a particular electrode or fluid deliveryport is facing. In this way, knowledge of the marker 76 of burr hole capassembly 70 that aligns with marker 36 of therapy delivery member 12 maybe used to derive the rotational orientation of the implanted therapydelivery member 12. In this way, markers 76 of burr hole cap assembly 70can be used after implanting therapy delivery member 12 and burr holecap assembly 70 in patient 14 and covering burr hole cap assembly 70with the scalp of patient 14 to determine the rotational orientation oftherapy delivery member 12 in patient 14. A clinician may, for example,identify the marker 76 that is known to align with marker 36 of therapydelivery member 12 and determine the orientation of marker 76 relativeto one or more target brain structures based on the known implantorientation of burr hole cap base 72.

In some examples, markers 76, and the respective labels, are radiopaque.In these examples, burr hole cap assembly 70 need not be implanted inpatient 14 in a known orientation in order to be able to later determinethe rotational orientation of therapy delivery member 12 in patient 14,e.g., after burr hole cap assembly 70 is covered by the patient's skin.Markers 76 may also be used to identify whether or not the implantedtherapy delivery member 12 has rotated post-implant. Moreover, marker 36on therapy delivery member 12 need not be radiopaque in order to laterdeter nine the rotational orientation of therapy delivery member 12 inpatient 14. Rather, at the time therapy delivery member 12 is implantedin patient 14, the clinician may only need to record (e.g., in ahandwritten note and/or in an electronic device) intimation thatidentifies the marker 76 that best aligns with marker 36 of therapydelivery member 12. The rotational orientation of therapy deliverymember 12 may be determined at a time following implantation of therapydelivery member 12 in patient 14 by, for example, imaging patient 14 toidentify the marker 76 that was recorded as being closest to marker 36of therapy delivery member 12 and determining the position of the marker76 relative to one or more brain structures of patient 14 or anotheranatomical landmark. In this way, in examples in which burr hole capassembly 70 includes radiopaque markers 76, burr hole cap assembly 70may be referenced at any time to determine a rotational orientation oftherapy delivery member 12 relative to one or more anatomical structuresof patient 14.

In other examples of burr hole cap assembly 70, markers 76 may notindicate the position on base 72 in terms of degrees, but, rather, mayuse other types of labels. For example, markers 76 may each beassociated with a respective number or other alphanumeric text. Asanother example, each marker 76 may be a different color. Markers 76have a characteristic that distinguishes each marker from an adjacentmarker, such that if a clinician indicates therapy delivery member 12 isaligned with a particular marker, the rotational orientation of therapydelivery member relative to base 72 can be determined by locating theparticular marker. In any of these examples, if base 72 is installed inburr hole 16 in a known orientation (e.g., with the 0° substantiallyaligning with a nose of a person), the markers are in known positionsrelative to burr hole 16, which is in a known position relative to oneor more brain structures. In this way, markers 76 may indicate therotational orientation of therapy delivery member 12 relative to burrhole cap assembly 70, from which the rotational orientation of therapydelivery member 12 relative to one or more brain structures of patient14 may be determined.

FIG. 7 is a flow diagram illustrating an example technique fordetermining a rotational position of therapy delivery member 12 relativeto a burr hole cap assembly with the aid of a base that includes aplurality of markers. While FIG. 7 is described with respect to burrhole cap assembly 70 (FIGS. 5 and 6), in other examples, the techniqueshown in FIG. 7 may be used with other burr hole cap assemblies with aplurality of markers.

In accordance with the technique shown in FIG. 7, a clinician mayintroduce therapy delivery member 12 through opening 30 in burr hole capbase 72 (86). For example, after burr hole cap base 72 is positionedover burr hole 16 (FIGS. 1 and 2) defined through cranium 18 of patient14, the clinician may introduce therapy delivery member 12 into patient14 through opening 30 in burr hole cap base 72. In some examples, theclinician utilizes a stereotactic equipment to guide one or more therapydelivery elements of therapy delivery member 12 to the one or moretarget tissue sites, e.g., in the brain of patient 14.

After therapy delivery member 12 is positioned as desired, the clinicianmay identify marker 36 on therapy delivery member 12 (88), e.g., byvisually ascertaining the location of marker 36. If therapy deliverymember 12 has more than one marker, the clinician may also identifythose markers, or just identify one marker 36. The clinician may thendetermine the marker 76 of base 72 that substantially aligns with marker36 of therapy delivery member 12 (90). The alignment may be, forexample, in a radial direction. For example, the clinician may determinewhich marker 76 of the plurality of markers 76 of base 72 is closest tomarker 36 of therapy delivery member 12.

In some examples, the clinician may record information that indicateswhich marker 76 of the plurality of markers 76 of base 72 substantiallyaligns with marker 36 of therapy delivery member 12. This informationmay then be later referenced to determine the rotational orientation ofan implanted therapy delivery member 12 in patient 14. In otherexamples, identification of the marker 76 of the plurality of markers 76of base 72 that substantially aligns with marker 36 of therapy deliverymember 12 may not be recorded for later retrieval, but may instead bedetermined on an as-needed basis, e.g., by imaging patient 14.

In other examples of burr hole cap assembly 70 and the technique shownin FIG. 7, markers 76 may be positioned on cover 74. In these examples,after positioning cover 74 over base 72, which may not only cover burrhole 16 but substantially fix therapy delivery member 12 in placerelative to base 72, the clinician may determine the marker on cover 74that aligns with marker 36 of therapy delivery member 12. In someexamples, marker 36 is identified prior to installation of cover 74(e.g., in examples in which cover 74 would completely cover marker 36),while in other examples, marker 36 is identified after installation ofcover 74 over base 72.

FIG. 8 is a conceptual illustration of another example burr hole capassembly 92, which includes base 94 with a plurality of markers 96 andset screw 98 that is movable relative to base 94. Base 94 may be similarto base 22 of burr hole cap assembly 20 (FIG. 1) in some examples.Although not shown in FIG. 8, in some examples, burr hole cap assembly92 may include a cover, similar to cover 24 of burr hole cap assembly 20(FIG. 1) that is configured to fit over base 94 and substantially closeopening 30 defined by base 94. Markers 96 may be similar to marker 76(FIGS. 5-7) in some examples. In the example shown in FIG. 8, however,markers 96 do not include any label or other characteristic (e.g., acolor) that distinguishes one marker 96 from another marker 96. Rather,markers 96 are substantially identical marks on base 94. In otherexamples, markers 96 may be similar to marker 76 (FIGS. 5-7) and mayinclude alphanumeric labels or be color coded.

Set screw 98 is configured to be introduced into cranium 18 of patient14. Set screw may have any suitable configuration. In some examples, setscrew 98 may be partially or fully threaded, and may comprise a headthat is wider than the threaded portion of set screw 98. In someexamples, set screw 98 is self-tapping, while in other examples, aseparate instrument may be used to define an opening in cranium 18 forreceiving set screw 98. Set screw 98 may be formed from any suitablematerial, such as, but not limited to, titanium, biocompatible polymers,or other biocompatible materials. In some examples, set screw 98comprises a radiopaque material, such that set screw 98 may be detectedby medical imaging after set screw 98 is covered by the patient's skin.

After therapy delivery member 12 is implanted in patient 14 through burrhole 16, which is accessed via opening 30 in base 94, a clinician mayplace set screw 98 in cranium 18 of patient 14 at a location thatindicates the rotational orientation of therapy delivery member 12. Inthe example shown in FIG. 8, for example, set screw 98 is implanted incranium 18 to indicate the location of marker 36 on therapy deliverymember 12. In particular, set screw 98 is substantially radially alignedwith marker 36 of therapy delivery member 12. In other examples, setscrew 98 may be implanted in cranium 98 to be slightly offset frommarker 36, i.e., not substantially radially aligned, but implanted in amanner that indicates the relative location of marker 36 of therapydelivery member 112. Moreover, in some examples, burr hole cap assembly92 may include more than one set screw 98. For example, two or more setscrews may be used to indicate the relative location of marker 36 oftherapy delivery member 12, e.g., marker 36 may be positioned midwaybetween the set screws. As another example, if therapy delivery member12 includes multiple markers, one or more set screws may be used toindicate the relative location of each of the markers of therapydelivery member 12.

Markers 96 of base 94 may be a visual aid to a clinician when theclinician inserts set screw 98 into cranium 18 of patient 14. Forexample, one or more markers 96 may define a visible line from marker 36of therapy delivery member 12 to a point on cranium 18 thatsubstantially radially aligns with marker 36, which may be the point atwhich the clinician may implant set screw 98. In other examples, base 94of burr hole cap assembly 92 may include any suitable number of markers,such as a fewer or greater number of markers than that shown in FIG. 8.In addition, in other examples, base 94 of burr hole cap assembly 92does not include markers 96.

In other examples, base 94 or a cap of burr hole cap assembly 92 may beconfigured to receive set screw 98 and set screw 98 may be configured tobe introduced into base 94 or the cap (e.g., instead of cranium 18) toindicate the rotational orientation of therapy delivery member 12. Forexample, base 94 or the cap may define preconfigured spots for set screw98 circumferentially located around the edge of base 94 or the cap, andafter therapy delivery member 12 is implanted in patient 14 through burrhole 16, a clinician may place set screw 98 in base 94 or the cap at alocation that indicates the rotational orientation of therapy deliverymember 12. In these examples, base 94 may or may not include markers 96.

FIG. 9 is a flow diagram illustrating an example technique determining arotational position of therapy delivery member 12 relative to a burrhole cap assembly that includes a set screw. While FIG. 9 is describedwith respect to burr hole cap assembly 92 (FIG. 8), in other examples,the technique shown in FIG. 9 may be used with other burr hole capassemblies that include one or more set screws.

In accordance with the technique shown in FIG. 9, a clinician mayintroduce therapy delivery member 12 through opening 30 in burr hole capbase 94 (100). For example, after burr hole cap base 94 is positionedover burr hole 16 (FIGS. 1 and 2) defined through cranium 18 of patient14, the clinician may introduce therapy delivery member 12 into patient14 through opening 30 in burr hole cap base 94. After therapy deliverymember 12 is positioned as desired, the clinician may identify marker 36on therapy delivery member 12 and a corresponding marker on base 94(102), e.g., by visually ascertaining the location of marker 36 and amarker 96 that best radially aligns with marker 36. The clinician maythen introduce set screw 98 in cranium 18, base 92, or another part ofassembly 92 proximate to the identified marker 96 on base 94 (104).

After therapy delivery member 12 is implanted in patient 14 and afterburr hole cap assembly 92 is covered up by the patient's skin, therotational orientation of therapy delivery member 12 may be determinedbased on information provided by set screw 98. In examples in which setscrew 98 comprises a radiopaque material, set screw 98 may be visible ina medical image. By identifying set screw 98 in the image, the clinicianmay also determine the orientation of therapy delivery member 12, i.e.,by determining that marker 36 is substantially aligned (e.g., radiallyaligned) with set screw 98. In other examples, markers 96 may bepositioned on a cover of burr hole cap assembly 92 In these examples,the clinician may insert set screw 98 in cranium 18 or the cap after thecover is placed over base 94.

If therapy delivery member 12 has more than one marker, and burr holecap assembly 92 includes more than one set screw, the technique shown inFIG. 9 may be repeated for the additional markers of therapy deliverymember 12.

Burr hole cap assembly 92 provides information that indicates therotational orientation of therapy delivery member 12 relative to burrhole cap assembly 92, which, as discussed above, may be used todetermine the orientation of one or more therapy delivery elements(e.g., electrodes or fluid delivery ports) in patient 14. Thisinformation may be obtainable from burr hole cap assembly 92 withoutimaging patient 14 after burr hole cap assembly 92 is covered by skin ofpatient 114. For example, in some examples, set screw 98 is implanted sothat it protrudes from cranium 18 and is detectable via palpation. Aclinician may palpate the patient's scalp to find set screw 98 and burrhole cap assembly 92. After finding set screw 98 and burr hole capassembly 92, the clinician may determine that therapy delivery member 12is implanted in patient 14 such that marker 36 faces set screw 98. Inthis way, the clinician may determine the direction in which the one ormore therapy delivery elements of therapy delivery member 12 face withinpatient 114, and relative to one or more brain structures of patient 14.

In some examples, set screw 98 comprises a radiopaque material, suchthat set screw 98 may be detected by medical imaging after set screw 98is covered by the patient's skin. In these examples, the clinician maydetermine the rotational orientation of therapy delivery member 12relative to burr hole cap assembly 92 by imaging patient 14 to determinethe location of set screw 98.

In addition, in some examples in which markers 96 are associated withunique identifiers (e.g., alphanumeric identifiers or a unique color),the clinician may record information that indicates which marker 96 ofthe plurality of markers 96 of base 94 substantially aligns with marker36 of therapy delivery member 12. If base 94 is implanted in burr hole16 in a known orientation or if markers 96 are radiopaque, thisinformation may then be later referenced to determine the rotationalorientation of one or more therapy delivery elements of an implantedtherapy delivery member 12 in patient 14.

FIG. 10A is a conceptual perspective view of another example burr holecap assembly 110, which includes base 112 and rotating member 114including a marker 116. FIG. 10B is a schematic and conceptualcross-sectional illustration of base 112, rotating member 114, andtherapy delivery member 12, where base 112 is implanted in burr hole 16in cranium 18 of patient 14. Base 112 defines opening 30 configured toreceive therapy delivery member 12. Although not shown in FIGS. 10A and10B, burr hole cap assembly 110 may include a cover, such as cover 24 ofburr hole cap assembly 20 (FIGS. 1 and 2), that is configured to fitover base 112 and rotating member 114 and substantially close opening 30defined by base 112. In some examples, the cover may also substantiallyfix a position of therapy delivery member 12 relative to base 112 androtating member 114.

Rotatable member 114 and base 112 may have similar cross-sectionalgeometries (e.g., circular in the example shown in FIGS. 10A and 10B) ordifferent cross-sectional geometries. Rotatable member 114 ismechanically coupled to base 112 and is configured to rotate relative tobase 112, e.g., around center axis 118 that is common to both base 112and rotatable member 114. For example, rotatable member 114 may bemounted to base 112 on bearings 1117, as shown in FIG. 10B. In additionor instead, rotatable member 1114 may be mounted to base 112 via a setof gears or friction fit bushings. As another example, rotatable member114 and base 112 may have similarly shaped surfaces that slidably engagesuch that rotatable member 114 may slide relative to base 112, whichmains relatively stationary relative to burr hole 16 (FIGS. 1 and 2). Insome examples, rotatable member 114 is configured to rotate in only onedirection relative to base 112. For example, rotatable member 114 may bemounted to base via a ratcheting mechanism. Rotatable member 114 may berotated continuously about axis 118 in some examples, while in otherexamples, rotatable member 114 has predetermined, discrete positionsrelative to base 112 (e.g., the positions associated with each toothboundary in the case of a ratcheting mechanism).

Burr hole cap assembly 110 includes a mechanism that substantially fixesthe rotational position of rotatable member 114 relative to base 1112.In examples in which rotatable member 114 is mounted to base 112 via aratcheting mechanism, for example, the ratcheting mechanism may includea spring loaded finger that engages with teeth of a gear; the rotationalposition of rotatable member 114 relative to base 112 may besubstantially fixed by the spring until a force sufficient to overcomethe spring force disengages the spring from the teeth. One or more othermechanisms may be used to substantially fix the rotational position ofrotatable member 114 relative to base 112, such as one or more setscrews, slide locks (e.g., comprised of a tooth on either member 114 orbase 1112 that slide engages notches on the other one of member 114 orbase 112), friction between rotatable member 114 and base 112, anadhesive, or crimping of rotatable member 114 to base 112 (e.g., via atool or by application of force by the clinician's fingers). Inaddition, in some examples, application of cover 24 of burr hole capassembly 110 may substantially lock rotating member 114 in placerelative to base 112.

Marker 116 may be similar to other markers 76 (FIGS. 5 and 6) andmarkers 96 (FIG. 8) described herein. In some examples, marker 116comprises a radiopaque material that is visible in a medical image. Inaddition, marker 116 can be visible to the human eye without the aid avisualization instrument. In some examples, marker 116 protrudes from amajor surface of rotating member 114, while in other examples, marker116 is substantially flush with rotating member 114.

Marker 116 has a fixed position relative to rotatable member 114, suchthat as rotatable member 114 rotates relative to base 112, marker 116moves relative to base 112. This configuration enables a clinician tomanipulate rotatable member 114 until marker 116 is positioned toindicate the rotational orientation of therapy delivery member 12relative to base 112.

FIG. 11 is a flow diagram of an example technique for indicating arotational position of therapy delivery member 12 relative to a burrhole cap assembly that includes a rotatable member with a marker, wherethe member rotates relative to a base of the burr hole cap assembly thatis configured to fit in a burr hole. While FIG. 11 is described withrespect to burr hole cap assembly 110, in other examples, the techniqueshown in FIG. 11 may be used with other burr hole cap assemblies.

In accordance with the technique shown in FIG. 11, a clinician mayintroduce therapy delivery member 12 through opening 30 in burr hole capbase 112 (120). For example, after base 112 is positioned over burr hole16 (FIGS. 1 and 2) defined through cranium 18 of patient 14 and base 112is substantially fixed relative to burr hole 16, the clinician mayintroduce therapy delivery member 12 into patient 14 through opening 30in base 112. After therapy delivery member 12 is positioned as desired,the clinician may identify marker 36 on therapy delivery member 12(122). Thereafter, the clinician may rotate rotatable member 114 untilmarker 116 substantially aligns (e.g., radially aligns) with marker 36(124). For example, the clinician may rotate rotatable member 114 untilmarker 116 is adjacent marker 36, as shown in FIG. 10A.

In some cases, therapy delivery member 12 may be implanted in patient 14such that marker 36 is not directly adjacent base 112 (as shown in FIG.10A.), but, rather, is positioned to be aligned with a part of base 112not in contact with therapy delivery member 12. For example, therapydelivery member 12 may be implanted in patient 14 such that marker 36 isrotated about 180° about a longitudinal axis of therapy delivery member12 relative to the orientation shown in FIG. 10A. In these cases, marker116 of rotatable member 114 may be relatively far from therapy deliverymember 12 (e.g., may be rotated about 180° about axis 118 relative tothe orientation shown in FIG. 10A), but may still indicate therotational orientation of therapy delivery elements of member 12 inpatient 14. Therapy delivery member 12 need not be directly adjacentmarker 114 of rotatable member 114 in order for the rotationalorientation of markers 36, 116 to be aligned.

After therapy delivery member 12 is implanted in patient 14 and afterburr hole cap assembly 110 is covered up by the patient's skin, therotational orientation of therapy delivery member 12 may be determinedbased on information provided by marker 116. In examples in which marker116 comprises a radiopaque material, marker 116 may be visible in amedical image. Thus, a clinician can generate a medical image of patient14 and burr hole cap assembly 110 and identify marker 116 in the medicalimage to determine the orientation of therapy delivery member 12relative to burr hole cap assembly base 112. In examples in which marker116 protrudes from assembly 110 or is otherwise detectable by palpation,the clinician may palpate patient 14 to determine the position of marker116.

The clinician may determine the rotational orientation of therapydelivery member 12 in patient 14 based on the information indicating theposition of marker 116 relative to, e.g., cranium 18 (FIG. 1) of patient14. For example, the clinician may determine that marker 36 issubstantially aligned (e.g., radially aligned) with marker 116, and maydetermine that burr hole cap assembly 110, including marker 116, has aknown orientation (in three dimensional space) relative to one or moreanatomical structures of patient 114. Thus, by relating the rotationalorientation of therapy delivery member 12 to burr hole cap assembly 110and relating the orientation of burr hole cap assembly 110 to one ormore anatomical structures of patient 14, the clinician may determinethe orientation of therapy delivery member 12 relative to one or moreanatomical structures of patient 14.

If therapy delivery member 12 includes a plurality of markers, theclinician may choose which marker of therapy delivery member 12 withwhich the marker 116 of burr hole cap assembly 110 should be aligned.The clinician may then record information that indicates the marker oftherapy delivery member 12 with which marker 116 is aligned.

FIG. 12 is a conceptual top view of burr hole cap assembly 130, whichincludes burr hole cap assembly base 132 and rotatable member 133. Alsoshown in FIG. 12 is a functional block diagram of reader device 142,which is described in further detail below. Burr hole cap assembly base132 may be similar to burr hole cap assembly base 112 (FIG. 10) anddefines opening 30 that is configured to receive a therapy deliverymember. Although not shown in FIG. 12, burr hole cap assembly 130 mayinclude a cover, which can be similar to cover 24 of burr hole capassembly 20 (FIG. 2). The cover may be configured to be mechanicallyconnected to base 132, and may also be configured to substantially fixtherapy delivery member 12 in place relative to burr hole 16 in cranium18 (FIG. 1), as well as substantially cover burr hole 16.

Burr hole cap assembly base 132 includes two reactive elements, which inthe example shown in FIG. 12, includes inductors 134, 136 electricallyconnected to at least one other electrical component (e.g., one or morecapacitors and/or resistors), such that each of the inductors 134, 136is a part of a respective circuit (separate circuits). Example reactiveelements including an inductor (e.g., inductor 134 or inductor 136) areshown in FIGS. 13A-13C and described in further detail below. Thecircuits in which inductors 134, 136 are included may be, for example,passive circuits that do not have their own power source. Rather, asdiscussed below, the circuits can be powered by an external device,e.g., via inductive coupling.

The circuits in which inductors 134, 136 are included may be, forexample, resonant circuits. For example, in some examples, each inductor134 is electrically connected to a capacitor, and, in some cases, aresistor, in parallel or in series to form an electrical harmonicoscillator, which is configured to store electrical energy oscillatingat a resonant frequency of the circuit. The inductive reactance of thecircuit may change as a function of the resonant frequency of theinductor 134 or 136 in the circuit, such that the resonant frequency ofthe circuit may be indicative of the inductive reactance of theinductor. One or both inductors 134, 136 may be configured to radiateenergy effectively when resonant, or the respective circuit may include(in addition to the inductive or capacitive elements), an antennaelement.

The resonant frequency of an inductor can be determined based on thefollowing equation:

XL=2*pi*f′L   (Equation 1)

In the above equation, XL is the inductive reactance, f is the resonantfrequency, and L is the inductance value of the inductor. The inductanceL of inductors 134, 136 are known values, e.g., are a property of theinductors 134, 136 that is known at the time the inductors 134, 136 arepositioned in base 132. Thus, if the resonant frequency of the inductoris determined, the value of the inductive reactance of the inductor maybe determined using Equation 1. In order to determine the rotationalorientation of marker 140 relative to base 132, a parameter indicativeof the inductive resonance can be determined, such as the resonantfrequency.

FIG. 13A is a schematic circuit diagram of an example reactive element155 that can be included in burr hole cap base 132. Reactive element 155includes inductor 156 and capacitor 157 connected in parallel, andvoltage source 158, which can be, for example, provided by an externaldevice (e.g., reader device 142 discussed in further detail below or amedical device programmer). Inductor 156 may be, for example, inductor134, 136 discussed above with respect to FIG. 12. Reactive element 155is configured to resonate when the reactances of inductor 156 andcapacitor 157 are substantially equal to each other.

The reactance of capacitor 157 can be determined based on the followingequation:

XC=1/(2*pi*f*C)   (Equation 2)

In the above equation, XC is the capacitive reactance, f is the resonantfrequency, and C is the capacitance value of the inductor. Theinductance C of capacitor 157 is a known values because it is a propertyof capacitor 157.

In some examples, reactive element 156 may include a coil and arectifier and the external power source may energize the coil andrectifier, rather than directly energizing the inductor. Thus, a currentcan be induced by an external magnetic field in the circuit includinginductor 156 through the coil and rectifier, which then apply thecurrent across inductor 156 and capacitor 157.

FIG. 13B is a schematic circuit diagram of another example reactiveelement 159 that can be included in burr hole cap base 132. Reactiveelement 159 includes inductor 156 and capacitor 157 connected inparallel, and resistor 160 connected in series with inductor 156. FIG.13C is a schematic circuit diagram of another example reactive element162 that can be included in burr hole cap base 132. Reactive element 162includes inductor 156 and capacitor 157 connected in series, andresistor 160 connected in parallel with capacitor 157.

In some examples, the circuits shown in FIGS. 13A-13C, as well as otherexample reactive elements, may be connected to an antenna coil thatcollects the energy from the circuit and allows resonance to occur. Inother examples, inductor 156 in the circuit may act as an antenna coil,and capacitor 157 and, in some examples, resistor 160, are selected toresonate at a desired frequency. For example, an external device (e.g.,reader device 142 or a programmer) may generate power that induces acurrent in inductor 156, which may then emit a resonant signal that issensed by the external device. A processor of the external device maythen determine a parameter indicative of the inductive reactance ofinductor 156 based on the resonant signal, e.g., based on the resonantfrequency or by using Equation 1 to determine the resonant frequency.

Returning now to FIG. 12, inductors 134, 136 and their respectivecircuits are in fixed positions relative to each other, as well asrelative to the body that defines base 132. Inductors 134, 136 of base132 are passive electrical components that, together with theircircuits, are configured to store energy in a magnetic field aselectrical current passes through respective conductors. Inductors 134,136 may each have any suitable configuration, and may be, but need notbe, identical in construction. In some examples, inductors 134, 136 eachcomprise an electrical conductor (e.g., copper wire or another type ofwire) shaped as a coil, thereby defining a conductive coil. Theconductor may be wrapped around air or a ferrous material in someexamples, although other types of inductors can also be used. The coilcan be circular in cross-section, quadrilateral (e.g., square orrectangular) in cross-section, or have any suitable cross-sectionalshape. Inductors 134, 136 may each be configured to be energized in thepresence of a magnetic field.

In the example shown in FIG. 12, rotatable member 133 may be similar torotatable member 114 (FIG. 10), but includes ferromagnetic marker 140,which is comprised of a ferromagnetic material. Rotatable member 133 maybe configured to rotate relative to base 132, e.g., using the mechanismsdescribed above with respect to member 114. Examples of suitableferromagnetic materials include, but are not limited to, iron (Fe),cobalt (Co), nickel (Ni), or any combinations thereof. In otherexamples, marker 140 can be comprised of other materials that affect theflow of magnetic fields. Marker 140 is visible to the human eye withoutthe aid of medical imaging, and, in some examples, may also beradiopaque.

Ferromagnetic marker 140 is at a fixed position on rotatable member 133,such that as rotatable member 133 rotates relative to base 132, marker140 rotates relative to base 132, and, therefore, relative to inductors134, 136. Ferromagnetic marker 140 is positioned at a predeterminedcircumferential position on rotatable member 133. Ferromagnetic marker140 may have any suitable dimension. The size and geometry offerromagnetic marker 140, as well as the placement on rotatable member133 (e.g., the distance relative to center axis 118 of cap 132) areselected such that marker 140 is configured to cause desired,appreciable changes in the inductive reactances of inductors 134, 136that can be sensed by a reader device, such as reader device 142, whichis discussed in further detail below. In some examples, the proximity ofmarker 140 to inductors 134, 136, the size of inductors 134, 136, andmaterial properties of ferromagnetic marker 140 may also affect theaffect of ferromagnetic marker 140 on the inductive reactances ofinductors 134, 136. Thus, in some cases, the configuration offerromagnetic marker 140 may be selected such that even when rotatablemember 133 is rotated to a position in which ferromagnetic marker 140 isas far from inductors 134, 136 as possible, marker 140 may still causeappreciable changes in the inductive reactances of inductors 134, 136.

As with marker 116 of rotatable member 114 (FIG. 10), ferromagneticmarker 140 can be substantially aligned with marker 36 of therapydelivery member 12 by rotating rotatable member 133, such that marker140 indicates the rotational orientation of therapy delivery member 12relative to base 132. After therapy delivery member 12 is introducedthrough opening 30 in base 132 and positioned in patient 14 as desired,the clinician may identify marker 36 on therapy delivery member 12 androtate rotatable member 133 until marker 140 substantially aligns (e.g.,radially aligns) with marker 36 (124). For example, the clinician mayrotate rotatable member 114 until marker 116 is adjacent marker 36, asshown in FIG, 12.

The proximity of ferromagnetic marker 140 to inductors 134, 136 maychange the inductive reactances of the inductors 134, 136. Depending onthe rotational orientation of rotatable member 133 relative to base 132,the proximity of ferromagnetic marker 140 to inductors 134, 136 maychange, and the proximity of ferromagnetic marker 140 to inductors 134,136 may change the inductive reactances of inductors 134, 136. On atleast this principle, the rotational orientation of therapy deliverymember 12 relative to base 132 may be determined with the aid of marker140.

In other examples, ferromagnetic marker 140 may not be visible and maybe positioned in (or on) rotatable member 133 at a fixed positionrelative to a visible marker (e.g., visible marker 116 shown in FIG.10A). In some examples, ferromagnetic marker 140 is not aligned with thevisible marker, while in other examples, ferromagnetic marker 140 isaligned (e.g., overlaps) with the visible marker. In either case, therotation of the visible marker relative to base 132 and inductors 134,136 may also result in rotation of ferromagnetic marker 140 relative toinductors 134, 136, which may cause detectable changes in the inductivereactances of inductors 134, 136 that can be sensed by a reader device,such as reader device 142. The changes in the inductive reactances ofinductors 134, 136 may be associated with a particular position of thevisible marker.

In addition, although one ferromagnetic marker 140 is shown in FIG. 12,in other examples, rotatable member 133 may include more than oneferromagnetic marker that is in fixed position relative to a visiblemarker, such that changes in the inductive reactances of inductors 134,136 caused by the position of the ferromagnetic markers may beassociated with a particular position of the visible marker.

To determine the inductive reactance of inductor 134, inductor 134 maybe energized and one or more properties (e.g., the magnetic flux) of themagnetic field generated by inductor 134 may be sensed. The energizationof inductor 134 causes current to flow in the conductive coil ofinductor 134 and the circuit of which inductor 134 is a part. Thecircuit including inductor 134 has a resonant frequency that is relatedto the inductive reactance of inductor 134 (see Equation 1 above), suchthat determining a frequency at which the circuit oscillates onceenergized allows the inductive reactance of the inductor 134 to bedetermined. In some examples, the frequency at which the circuitoscillates may be determined by monitoring the magnetic or electricfields the circuit radiates back to the energizing system, which may bereader device 142 in some examples, and determining a frequency of theoscillation of electrical and/or magnetic components of theelectromagnetic field. The inductive reactance of inductor 136 cansimilarly he determined.

In some examples, marker 140 may be designed in a way so as to minimallyinterfere with MRI scans, e.g., by appropriately adjusting theconfiguration (e.g., size, shape, material, or any combination thereof)of marker 140 or a mechanism of action by which marker 140 indicates therotational orientation of therapy delivery element 12. For example, asecond coil may be used to load a primary coil, but tuned such that MRIinteraction is minimized, e.g., to cause less distortion in a magneticresonance environment.

In some examples, a reader device 142 can be used to determine theinductive reactance of each of the inductors 134, 136. Reader device1.42 shown in FIG, 12 includes processor 144, memory 146, coil 148,sensor 150, power source 152, and user interface 154. Reader device 142comprises any suitable arrangement of hardware, alone or in combinationwith software and/or firmware, to perform the techniques attributed toreader device 142. In various examples, processor 144 may include one ormore processors, such as one or more microprocessors, controllers,digital signal processors (DSPs), application specific integratedcircuits (ASICs), field-programmable gate arrays (FPGAs), or equivalentdiscrete or integrated logic circuitry. Memory 146 may include, forexample, any volatile or non-volatile media, such as a random accessmemory (RAM), read only memory (ROM), non-volatile RAM (NVRAM),electrically erasable programmable ROM (EEPROM), flash memory, and thelike. Although processor 144, coil 148, and sensor 150, are described asseparate modules, in some examples, processor 144, coil 148, and sensor150 can be functionally integrated. In some examples, processor 144,coil 148, and sensor 150 correspond to individual hardware units, suchas ASICs, DSPs, FPGAs, or other hardware units. Power source 152delivers operating power to the components of reader device 142. Powersource 152 may include a rechargeable or non-rechargeable battery and apower generation circuit to produce the operating power.

Under the control of processor 144, coil 148 (e.g., an inductor similarto one or both inductors 134, 136) is energized with power from powersource 152 to generate a magnetic field (or electric field in someexamples) that is configured to energize a proximate inductor 134, 136.In addition, under the control of processor 14, sensor 150 senses themagnetic flux or other property of the magnetic field generated by theenergized inductor 134 or 136, which can indicate the inductivereactance of the inductor 134, 136. For example, processor 144, with theaid of sensor 150, may determine the frequency at which the circuitincluding the inductor 134, 136 being monitored oscillates onceenergized by monitoring the magnetic or electric fields the circuitradiates back to sensor 150. As discussed above, the frequency ofoscillation (also referred to as a resonant frequency) is indicative ofthe inductive reactance of the respective inductor 134 or 136 (seeEquation 1). As a result, once processor 144 determines the resonantfrequency of the circuit, the inductive reactance may be determinedusing Equation 1 and the known inductance value of the respectiveinductor 134, 136.

As discussed in detail below, a parameter indicative of the inductivereactance of the inductor can be associated with a particular rotationalposition of marker 140 relative to base 132, where the parameter can be,for example, the resonant frequency, the inductive reactance, a ratio ofresonant frequencies of inductors 134, 136, a ratio of inductivereactances of inductors 134, 136, and the like. That is, each of aplurality of rotational positions of marker 140 may be associated with aunique parameter indicative of the inductive reactance. Accordingly,processor 144 may access a data structure or the like to determine therotational position of marker 140 relative to base 132 associated withthe determined parameter indicative of the inductive reactance of theinductor. Based on Equation 1, the resonant frequency may be directlyindicative of the inductive reactance, such that the frequency may be asurrogate for the inductive reactance.

In some examples, coil 148 can be used to both energize inductors 134,136 and sense the properties of each of the magnetic fields generated bythe energized inductors 134, 136, i,e., in some examples, sensor 150 maycomprise coil 148. In some examples, memory 146 stores the values ofsensed resonant frequencies, determined inductive reactance values,other values related to determining the rotational orientation of marker140 relative to base 132, as well as any software necessary for theoperation of reader device 142.

In some examples, user interface 154 may include a display screen andone or more input buttons that allow reader device 142 to receive inputfrom a user. In some examples, the display may be, for example, a liquidcrystal display (LCD), light emitting diode (LED) display, or a touchscreen. The input buttons may include a touch pad, increase and decreasebuttons, emergency shut off button, alphanumeric keypad or a reduced setof keys associated with particular functions, and/or other buttonsneeded to control interrogation of inductors 134, 136 and otherfunctions provided by reader device 142. In some cases, the user mayinteract with user interface 154 via a stylus, soft keys, hard keys,directional devices, and any of a variety of other input media.

A user may interact with user interface 154 to control reader device142. For example, in some examples, user interface 154 may compriseinput buttons or the like that enable a user to initiate theinterrogation of inductors 134, 136, store the determined inductivereactances of inductors 134, 136, determine the relative orientation oftherapy delivery member 12 relative to base 132 based on the determinedinductive reactances, and the like. In addition, in some examples,processor 144 controls user interface 154 to provide information to theuser. For example, processor 144 may display determined inductivereactances values (or ratio of values) via the display screen of userinterface 154. As another example, processor 144 may display, via thedisplay screen of user interface 154, the distances between markers 140and inductors 134, 136, the ratio of such distances, or rotationalorientation of marker 140 determined by processor 144 based ondetermined inductive reactance values or sensed resonant frequencies.

In some examples, the inductive reactance of inductor 134 can beassociated with a distance between ferromagnetic marker 140 and inductor134 and the inductive reactance of inductor 136 can be associated with adistance between ferromagnetic marker 140 and inductor 136. Thus, insome examples, a plurality of inductive reactance values and associateddistances can be predetermined and stored (e.g., by memory 146 of readerdevice 142 or another external device, or by an implanted device, suchas a medical device) for each inductors 134, 136. The stored distancescan be radial in some examples in which base 132 and rotatable member133 are substantially circular in cross-section. In other examples, thestored distances can be linear.

The distances between marker 140 and inductors 134, 136 are based on therotational orientation of rotatable member 133 relative to inductors134, 136. For example, as rotatable member 133 is rotated in a clockwisedirection relative to the rotational orientation shown in FIG. 12, thedistance between marker 140 and inductor 134 may increase, while thedistance between marker 140 and inductor 136 may decrease. Thus, whenmarker 140 is substantially aligned with marker 36 of therapy deliverymember 12, various values determined based on the inductive reactancesof inductors 134, 136 may be used to approximate the rotationalorientation of therapy delivery member 12 relative to base 132. Forexample, in one example, the ratio of the distance between marker 140and inductor 134 to the distance between marker 140 and inductor 136 maybe used to approximate the rotational orientation of marker 140 (and,therefore, therapy delivery member 12) relative to base 132.

As another example, a ratio of the inductive reactances of inductors134, 136 may be used to approximate the rotational orientation of marker140 relative to base 132. In yet another example, the absolute inductivereactance values of inductors 134, 136 or the individual distance valuesbetween marker 140 and inductors 134, 136 may be associated with aspecific rotational orientation of marker 140 relative to base 132. Inother examples, the sum of distances of marker 140 from each of theinductors 134, 136 can be associated with the approximate rotationalorientation of therapy delivery member 12 relative to base 132. Thus, aplurality of rotational orientations of marker 140 (e.g., expressed interms of degrees around the circular perimeter of base 132, where the 0°degree mark is at a known position of base 132, expressed in terms ofradians, or sectors or quadrants of base 132) can be associated with anyone or more of respective inductive reactance values of each ofinductors 134, 136, a respective ratio of inductive reactance values ofinductors 134, 136, a ratio of distances between marker 140 and eachinductor 134, 136, the sum of distances between marker 140 and eachinductor 134, 136 and the like. These values may be stored by memory 146of reader device 142 or by another device.

Determining the distances between ferromagnetic marker 140 of rotatablemember 133 and two inductors 134, 136 of burr hole cap assembly 130 mayhelp better approximate the rotational orientation of ferromagneticmarker 140 relative to base 132 compared to burr hole cap assembliesthat include only one inductor. The inductive reactances of inductors134, 136 may indicate not only the distance between one or bothinductors 134, 136 and marker 140, but also the direction of marker 140relative to inductors 134, 136. On the other hand, an inductivereactance of a single inductor 134 may indicate that marker 140 is acertain distance way, but may not indicate which direction (e.g.,clockwise or counterclockwise) the distance is measured. In addition,with one inductor, ferromagnetic marker 140 may have a similar effect onthe inductive reactance of the inductor when marker 140 is at twodifferent positions that are about 180° apart from each other (e.g., the6 o'clock and 12 o'clock positions if the outer perimeter of base 132represents the outer perimeter of a clock) and equidistant from theinductor. As a result, the inductive reactance of the inductor in thiscase would indicate marker 140 is at one of two possible rotationalpositions. On the other hand, with two inductors unevenly distributed(e.g., less than 180 degrees apart, such as at about the 4 o'clockposition and the 8 o'clock position) around base 132, ferromagneticmarker 140 can be at two different positions about 180 degrees apartfrom each other and result in different inductive reactances of theinductors, thereby making the position of the marker 140distinguishable.

A burr hole cap assembly that includes three or more inductors withrespective circuits may enable a triangulation solution for determiningthe position of ferromagnetic marker 140. While three, four or moreinductors may be redundant in some cases, the use of four or moreinductors to determine the rotational position of marker 40 relative tobase 132 may be useful in increasing accuracy of the rotational positiondetermination, such as by enabling a higher resolution of rotationalposition determination. In addition, the use of four or more inductorsmay also be useful fir detecting a smaller ferromagnetic marker. Asdiscussed above, the configuration of ferromagnetic marker 140,including the size, may affect how it affects the inductive reactancesof inductors 134, 136 of base 132.

In some cases, other ferromagnetic or electromagnetic elements of theenvironment may interfere with the inductive reactance of a reactiveelement. The use of more than two inductors can also enable processor144 to minimize the possibility of inaccurately determining therotational position of marker 140 relative to base 132, e.g., bycomparing the position determined based on different sets of reactiveelements and/or validating one position determined based on one or morereactive elements with another position determined based on differentone or more reactive elements.

In other examples, base 132 may include one inductor, two inductors, ormore than two inductors, and the rotational orientation of ferromagneticmarker 140 of rotatable member 133 relative to base 132 may bedetermined based on the inductive reactance of the one inductor or themore than two inductors.

FIG. 14 is a flow diagram of an example technique for determining arotational orientation of therapy delivery member 12 relative to base132 of burr hole cap assembly 130. The technique shown in FIG. 14 may beimplemented, for example, after therapy delivery member 12 is implantedin patient 14, and after burr hole cap assembly 130 is covered, e.g., bythe patient's scalp. Thus, burr hole cap assembly 130 may be an elegantway of determining the rotational orientation of therapy delivery member12 relative to base 132 of burr hole cap assembly 130 even after burrhole cap assembly 130 is not relatively easily accessible. Although thetechnique shown in FIG. 14 is described with respect to burr hole capassembly 130, in other examples, other burr hole cap assemblies with oneor more inductors may be used in a similar manner to determine arotational orientation of therapy delivery member 12 relative to base132 of burr hole cap assembly 130 after therapy delivery member 12 isimplanted in patient 14, and after burr hole cap assembly 130 iscovered, e.g., by the patient's scalp.

In accordance with the technique shown in FIG. 14, the inductivereactance of a first inductor 134 of burr hole cap assembly 130 isdetermined (170). In some examples, a user may utilize reader device 142to interrogate inductor 134 to determine the inductive reactance ofinductor 134. The user may place reader device 142 near burr hole capassembly 130 (e.g., adjacent the patient's scalp near burr hole capassembly 130). As discussed above, coil 148 of reader device 142 maygenerate a magnetic field that energizes inductor 134. When inductor 134is energized, sensor 150 may sense one or more properties of themagnetic field generated by inductor 134, where the properties areindicative of the inductive reactance of inductor 134. Processor 144 ofreader device 142 or another device (e.g., a medical device programmer,a computing device utilized by a clinician or the like) may thendetermine the inductive reactance of inductor 134 based on the one ormore sensed properties of the magnetic field generated by inductor 134in response to the energization. The inductive reactance of a secondinductor 136 of burr hole cap assembly 130 can be determined (172),e.g., in a similar manner as that discussed above with respect toinductor 134.

The inductive reactance of each of the inductors 134, 136 may bedetermined at separate times in some examples, or at the same time inother examples. After determining the inductive reactances of theinductors 134, 136, the rotational orientation of therapy deliverymember 12 relative to base 132 can be determined based on the determinedinductive reactances (174). In one example, processor 144 of readerdevice 142 determines a ratio of the distance between ferromagneticmarker 140 of rotatable member 133 and inductor 134 to the distancebetween ferromagnetic marker 140 and inductor 136 and determines therotational orientation of marker 140 relative to base 132 associatedwith the determined ratio in memory 146 of reader device 142.

In another example, processor 144 determines the absolute values of theinductive reactances of inductors 134, 136, which may in some casesindicate the rotational position of marker 140 better than the ratio ofinductive reactances. For example, when marker 140 is positionedequidistant from both inductors 134, 136 (e,g., when marker 140 is ateither the 6 o'clock or 12 o'clock position when inductors 134, 136 areat the 4 o'clock and 8 o'clock positions, respectively), the ratio ofthe inductive reactances may not indicate which of these two rotationalpositions marker 140 is positioned, whereas marker 140 at theequidistant position that is closer to inductors 134, 136 (e.g., the 6o'clock position versus the 12 o'clock position) may have a largerimpact on the inductive reactances of inductors 134, 136 than the otherequidistant position. In this way, the absolute inductive reactancevalues of the inductors 134, 136 may be used to determine the rotationalposition of marker 140 in some examples. Because marker 140 issubstantially aligned with marker 36 of therapy delivery member 12, thedetermined rotational orientation of ferromagnetic marker 140 relativeto base 132 may be substantially the same, or at least indicative of therotational orientation of therapy delivery member 12 relative to base132.

In other examples, burr hole cap assembly 130 (e.g., base 132 or a cap)may have radiopaque elements that allow its orientation and location tobe registered to anatomical images of patient 14. The rotationalposition of ferromagnetic marker 140 (or a visible marker in a fixedposition relative to ferromagnetic marker 140) can then be used to findthe rotational orientation of therapy delivery member 12 relative to thebrain of patient 14.

As discussed above, base 132 may be implanted in a known orientationrelative to brain of patient 14, such that the position of inductors134, 136 relative to one or more target brain structures may bedetermined. As a result, once the rotational orientation of marker 140relative to base 132 is determined, the orientation of one or moretherapy delivery elements of therapy delivery member 12 relative to oneor more target brain structures of patient 14 may be determined.

In other examples, other mechanisms can be used to change the inductanceof one or more inductors of a burr hole cap assembly such that theinductance is indicative of the rotational orientation of a therapydelivery member relative to the burr hole cap assembly. In the examplediscussed with respect to FIGS. 12 and 13, an element of rotatablemember 133 is implemented to change the response of the inductors 134,136. In other examples, a geometry of an inductor of a burr hole capassembly may be configured to change (directly in some examples orindirectly in others) as a function of the rotational orientation of atherapy delivery member relative to the burr hole cap assembly, wherethe geometry affects the inductance of the inductor. Thus, theinductance of the inductor may indicate the rotational orientation of atherapy delivery member relative to the burr hole cap assembly.

As an example, in one example, an inductor of the burr hole cap assemblymay have an adjustable core that is configured to move relative to acoiled conductor of the inductor. As the core moves different distancesin and out of the coil (e.g., the core may fit within the space definedby the inner perimeter of the coil), the inductance of the inductor maychange. The core of the inductor may be configured such that therelative position of the core and the coiled conductor is indicative ofthe rotational orientation of a therapy delivery member relative to theburr hole cap assembly. Accordingly, the inductance of the inductor maychange as a function of the rotational orientation of a therapy deliverymember relative to the burr hole cap assembly.

For example, a burr hole cap assembly may include a rotatable member(e.g., similar to rotatable member 114 shown in FIG. 10) that isconfigured to rotate relative to abuse, and the rotatable member may beconfigured such that as it rotates relative to the base, the adjustablecore moves relative in or out of the coil defined by the coiledconductor of the inductor, depending on which way the rotatable memberis rotated. The movement of the adjustable core relative to the coiledconductor may be proportional to the movement of the rotatable memberrelative to the base in some examples. The inductor can be mechanicallycoupled to the base in some examples, and may only be mechanicallyconnected to the rotatable member in other examples.

The rotatable member may include a first marker that is in a fixedposition on the rotatable member. After a therapy delivery member isintroduced through an opening defined by the base of the burr hole capassembly, a clinician can rotate the member to substantially align thefirst marker with marker 36 on therapy delivery member 12, e.g., asdescribed above with respect to rotatable member 114 shown in FIG 10.Thus, the clinician can manipulate the first marker until it isindicative of the rotational orientation of therapy delivery member 12.The marker on the therapy delivery member need not be ferromagnetic inthis example. Due to the mechanical coupling between the adjustable coreof the inductor and the rotatable member of the burr hole cap assemblymovement of the rotatable member to align the marker on the rotatablemember with marker 36 on therapy delivery member 12 incidentally movesthe core of the inductor relative to the coiled conductor. Accordingly,after therapy delivery member 12 is implanted patient 14 and is nolonger visible without the aid of medical imaging, the rotationalorientation of therapy delivery member 12 can be determined byinterrogating the inductor (e.g., with reader device 142 shown in FIG.12) to determine its inductance.

The inductance of the inductor is indicative of the position of the corerelative to the coiled conductor, which is indicative of the rotationalorientation of the first marker of the rotatable member. As discussedabove, the first marker can be substantially aligned with marker 36 oftherapy delivery member 12, such that the position of the first markerof the rotatable member is indicative of the position of marker 36.Because the orientation of the burr hole base relative to the patient'scranium 18 and the position of marker 36 relative to therapy deliveryelements of member 12 are known, the rotational orientation of thetherapy delivery elements relative to the cranium 18 may be determinedbased on the inductance of the inductor.

In some examples, a device (e.g., reader device 142, another externalcomputing device, or an implanted device) can store a plurality ofinductance values of the inductor and associate the inductance valueswith different rotational positions of the first marker. Theserotational positions may be indicated with respect to, for example, aknown anatomical landmark (e.g., the 0° rotational position may besubstantially aligned with the patient's nose) when the base of the burrhole cap assembly is implanted in a known orientation relative to theanatomical landmark. Thus, in some examples, a processor and/orclinician can determine the rotational orientation of therapy deliverymember 12 in a brain of patient 14 by determining the inductance of aninductor of the burr hole cap assembly, and determining the rotationalposition associated with the inductance. Moreover, in this example, theburr hole cap assembly is configured to transmit an indication (e.g., aninductance) that is indicative of the rotational orientation of atherapy delivery member relative to the burr hole cap assembly

In another example of a burr hole cap assembly that comprises aninductor with a geometry that is configured to change as a function ofthe rotational orientation of a therapy delivery member relative to theburr hole cap assembly, a burr hole cap assembly may comprise arotatable member (e.g., similar to rotatable member 114 shown in FIG.10) that is configured to rotate relative to a base, and the rotatablemember may be configured such that as it rotates relative to the base,the portion of the conductor of the inductor that is coiled changes,e.g., the length of the coiled conductor increases or decreasesdepending on which way the rotatable member is rotated. For example, theends of the conductor may be mechanically connected to the rotatablemember, such that the rotational orientation of the rotatable memberrelative to the base changes the position of the ends of the conductorrelative to, e.g., the center axis of the coil defined by the conductor.Again, the inductor can be mechanically coupled to the base in someexamples, and may only be mechanically connected to the rotatable memberin other examples.

The increase or decrease in the length of the coiled conductor may beproportional to the movement of the rotatable member relative to thebase in some examples. As described in further detail below, therotatable member may be rotated to a position to indicate the rotationalorientation of therapy delivery member 12 relative to the burr hole capassembly; such that the length of the coiled conductor is alsoindicative of the rotational orientation of therapy delivery member 12relative to the burr hole cap assembly. Because the length of the coiledconductor may affect the inductance of the inductor, the inductance ofthe inductor may change as a function of the rotational orientation oftherapy delivery member 12 relative to the burr hole cap assembly.

As with the previously described example, in this example, the rotatablemember may include a first marker that is in a fixed position on therotatable member. After therapy delivery member 12 is introduced throughan opening defined by the base of the burr hole cap assembly, aclinician can rotate the member to align the first marker with marker 36on the therapy delivery member, e.g., as described above with respect torotatable member 114 shown in FIG. 10. Marker 36 on therapy deliverymember 12 need not be ferromagnetic in this example. Due to themechanical coupling between the coiled conductor and the rotatablemember of the burr hole cap assembly, movement of the rotatable memberto align the marker on the rotatable member with marker 36 on therapydelivery member 12 incidentally changes the length of the coiled portionof the conductor. Accordingly, after therapy delivery member 12 isimplanted in patient 14 and is no longer visible without the aid ofmedical imaging, the rotational orientation of therapy delivery member12 can be determined by interrogating the inductor (e.g., with readerdevice 142 shown in FIG. 12) to determine its inductance.

The inductance of the inductor is indicative of the length of the coiledportion of the conductor, which is indicative of the rotationalorientation of the first marker of the rotatable member. Because theposition of the first marker of the rotatable member is indicative ofthe position of marker 36 of therapy delivery member 12 and theorientation of the base of the burr hole cap assembly relative to thepatient's cranium 18 is known, the rotational orientation of therapydelivery member 12 relative to the patient's cranium 18 may bedetermined based on the inductance of the inductor.

As with the previous example, in some examples, a device (e.g., readerdevice 142, another external computing device, or an implanted device)can store a plurality of inductance values of the inductor and associatethe inductance values with different rotational positions of the firstmarker. Thus, in some examples, a processor and/or clinician candetermine the rotational orientation of therapy delivery member 12 in abrain of a patient by determining the inductance of an inductor of theburr hole cap assembly, and determining the rotational positionassociated with the inductance. In this example, the burr hole capassembly is configured to transmit an indication (e.g., an inductance)that is indicative of the rotational orientation of a therapy deliverymember relative to the burr hole cap assembly.

In another example, a burr hole cap assembly can include a capacitiveelement that has a configuration, and, therefore, capacitance, thatchanges as a function of the rotational orientation of a therapydelivery member relative to the burr hole cap assembly. The capacitiveelement can include a dielectric between capacitor plates. In thisexample, a burr hole cap assembly may comprise a rotatable member (e.g.,similar to rotatable member 114 shown in FIG. 10) that is configured torotate relative to a base, and the rotatable member may be configuredsuch that as it rotates relative to the base, the dielectric and platesmove relative to each other. For example, the dielectric portion of thecapacitive element may be mechanically connected to the rotatable membersuch that the dielectric portion moves relative to two plates as therotatable member is rotated relative to the base. As another example,the plates of the capacitive element may be mechanically connected tothe rotatable member and may, e.g., move closer together or furtherapart from each and other and relative to the dielectric, depending onthe direction in which the rotatable member is rotated.

In either case, the movement of the dielectric or plates may beproportional to the movement of the rotatable member relative to thebase. When the clinician rotates the rotatable member to a position toindicate the rotational orientation of therapy delivery member 12relative to the burr hole cap assembly, the capacitance of thecapacitive element changes due to the change in the position of thedielectric or plates. As a result, the capacitance of the capacitiveelement may uniquely indicate the rotational orientation of a marker onthe rotatable member (which may be aligned with marker 36 on therapydelivery member 12). Accordingly, after therapy delivery member 12 isimplanted in patient 114 and is no longer visible without the aid ofmedical imaging, the rotational orientation of therapy delivery member12 can be determined by interrogating the capacitive element (e.g., withreader device 142 shown in FIG. 12) to determine its capacitance. Adevice (e.g., reader device 142, another external computing device, oran implanted device) can store a plurality of capacitance values of thecapacitive element and associate parameters indicative of thecapacitance (e.g., capacitance values) with different rotationalpositions of the marker on the rotatable member.

In examples in which a device, such as reader device 142, determines arotational orientation of therapy delivery member 12 relative to a burrhole cap assembly, the device may be configured to communicate thisinformation (e.g., via a wired or wireless communication technique) toother components (e.g., an implantable medical device or medical deviceprogrammer) for further programming and decision making

While FIGS. 12 and 13 describe examples in which a burr hole capassembly includes at least one inductor whose inductance can beindicative of a rotational orientation of a therapy delivery member, inother examples, a burr hole cap assembly can include one or more othertypes of reactive elements in addition to or instead of the reactiveelements including an inductor, capacitive element, or both, where theimpedance (or capacitance) of the one or more reactive elements isindicative of the rotational orientation of the therapy delivery memberrelative to the burr hole cap.

The techniques described in this disclosure, including those attributedto reader device 142, computing devices, or various constituentcomponents, may be implemented, at least in part, in hardware, software,firmware or any combination thereof. For example, various aspects of thetechniques may be implemented within one or more processors, includingone or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalentintegrated or discrete logic circuitry, as well as any combinations ofsuch components, embodied in programmers, such as physician or patientprogrammers, stimulators, image processing devices or other devices. Theterm “processor” or “processing circuitry” may generally refer to any ofthe foregoing logic circuitry, alone or in combination with other logiccircuitry, or any other equivalent circuitry.

Such hardware, software, and/or firmware may be implemented within thesame device or within separate devices to support the various operationsand functions described in this disclosure. Thus, techniques describedherein are primarily described as being performed by a specificprocessor, any one or more parts of the techniques described herein maybe implemented by a processor of any suitable computing device, alone orin combination with each other. In addition, any of the described units,modules or components may be implemented together or separately asdiscrete but interoperable logic devices. Depiction of differentfeatures as modules or units is intended to highlight differentfunctional aspects and does not necessarily imply that such modules orunits must be realized by separate hardware or software components.Rather, functionality associated with one or more modules or units maybe performed by separate hardware or software components, or integratedwithin common or separate hardware or software components.

When implemented in software, the functionality ascribed to the systems,devices and techniques described in this disclosure may be embodied asinstructions on a computer-readable medium such as RAM, ROM, NVRAM,EEPROM, FLASH memory, magnetic data storage media, optical data storagemedia, or the like. The instructions may be executed to support one ormore aspects of the functionality described in this disclosure.

Various examples have been described. These and other examples arewithin the scope of the following claims.

1. A system comprising: a base that is configured to fit inside of aburr hole in a cranium of a patient, wherein the base defines an openingthat is configured to receive a therapy delivery member; a marker thatis configured to indicate a rotational orientation of the therapydelivery member relative to the base; and a cover that is configured tosubstantially cover the opening defined by the base.
 2. The system ofclaim 1, wherein the cover is configured to substantially fix a positionof the therapy delivery member relative to the base when the therapydelivery member is received in the opening defined by the base.
 3. Thesystem of claim 1, wherein the marker comprises a visible markerpositioned on the base.
 4. The system of claim 1, wherein the markercomprises a radiopaque marker.
 5. The system of claim 1, wherein themarker comprises a first marker, the system comprising a plurality ofmarkers, wherein the first marker and the plurality of markers indicaterespective positions around the base.
 6. The system of claim 1, furthercomprising a rotatable member that is configured to rotate relative tothe base, wherein the rotatable member comprises the marker.
 7. Thesystem of claim 1, wherein the marker comprises an indicator elementthat is configured to be introduced in the cranium of the patient or thebase at a position that indicates the rotational orientation of thetherapy delivery member relative to the base, wherein the indicatorelement is movable relative to the base and the cover.
 8. The system ofclaim 7, wherein the indicator element is radiopaque.
 9. The system ofclaim 1, further comprising an inductor, wherein at least one of aninductive reactance or an inductance of the inductor is indicative of arotational orientation of the marker relative to the base.
 10. Thesystem of claim 9, further comprising a reader device that is configuredto determine a parameter indicative of the inductive reactance of theinductor,
 11. The system of claim 9, further comprising a rotatablemember that comprises the marker and the inductor, the rotatable memberbeing rotatable relative to the base, wherein the at least one of theinductive reactance or the inductance of the inductor changes based on arotational position of the rotatable member relative to the base. 12.The system of claim 11, wherein the inductor comprises a conductive coiland a core movable relative to the conductive coil, and wherein therotatable member is mechanically connected to the core and configuredsuch that rotation of the rotatable member relative to the base movesthe core relative to the conductive coil.
 13. The system of claim 11,wherein the inductor comprises a conductive coil mechanically connectedto the rotatable member, and wherein rotation of the rotatable memberrelative to the base changes a length of the conductive coil.
 14. Thesystem of claim 1, further comprising: a capacitive element; and arotatable member that comprises the marker and the capacitive element,the rotatable member being rotatable relative to the base, wherein acapacitance of the capacitive element changes based on a rotationalposition of the rotatable member relative to the base.
 15. The system ofclaim 1, wherein the marker comprises a ferromagnetic material, thesystem further comprising: an inductor within the base; and a rotatablemember that comprises the marker, the rotatable member being rotatablerelative to the base, wherein the inductance of the inductor changesbased on a rotational position of the marker relative to the base. 16.The system of claim 1, wherein the marker comprises a first marker, thesystem further comprising the therapy delivery member comprising asecond marker, the first marker being configured to be moved relative tothe base to substantially align with the second marker.
 17. The systemof claim 1, further comprising: the therapy delivery member, wherein thetherapy delivery member comprises the marker, the marker beingferromagnetic; and an inductor within the base, wherein a proximity ofthe marker to the inductor indicates a rotational orientation of thetherapy delivery member relative to the base.
 18. A method comprising:introducing a therapy delivery member through an opening defined by abase of a burr hole cap assembly, wherein the base is configured to fitinside of a burr hole in a cranium of a patient; and indicating arotational orientation of the therapy delivery member relative to thebase with a marker of the burr hole cap assembly.
 19. The method ofclaim 18, wherein the marker comprises a first marker, and indicatingthe rotational orientation of the therapy delivery member relative tothe base comprises: locating a second marker on the therapy deliverymember; and locating, from among of plurality of markers that are atdifferent positions around a perimeter of the base, the first markerthat substantially aligns with a second marker.
 20. The method of claim18, wherein the marker comprises a first marker and the therapy deliverymember comprises a second marker, and wherein indicating the rotationalorientation of the therapy delivery member relative to the basecomprises rotating a rotatable member that comprises the first marker tosubstantially align the first marker with the second marker, wherein therotatable member is rotatable relative to the base.
 21. The method ofclaim 20, wherein the rotatable member comprises an inductor, wherein atleast one of an inductive reactance or an inductance of the inductor isindicative of a rotational orientation of the first marker relative tothe base, the method further comprising, after introducing the therapydelivery member through the opening defined by the base, determining therotational orientation of the therapy delivery member relative to thebase by at least determining a parameter indicative of the at least oneof the inductive reactance or the inductance of the inductor.
 22. Themethod of claim 21, wherein the inductor comprises a conductive coil anda core movable relative to the conductive coil, and wherein therotatable member is mechanically connected to the core and configuredsuch that rotation of the rotatable member relative to the base movesthe core relative to the conductive coil.
 23. The method of claim 21,wherein the inductor comprises a conductive coil mechanically connectedto the rotatable member, and wherein rotation of the rotatable memberrelative to the base changes a length of the conductive coil.
 24. Themethod of claim 20, wherein the rotatable member comprises a capacitiveelement, wherein a capacitance of the capacitive element changes basedon a rotational position of the rotatable member relative to the base,the method further comprising, after introducing the therapy deliverymember through the opening defined by the base, determining therotational orientation of the therapy delivery member relative to thebase by at least determining a parameter indicative of the capacitanceof the capacitive element.
 25. The method of claim 18, whereinindicating the rotational orientation of the therapy delivery memberrelative to the base comprises introducing the marker into the craniumof the patient or the base at a position that indicates the rotationalorientation of the therapy delivery member relative to the base.
 26. Themethod of claim 18, wherein introducing the therapy delivery memberthrough the opening defined by the base comprises implanting the therapydelivery member in a brain of the patient, the method furthercomprising, after implanting the therapy delivery member in the brain ofthe patient, determining the rotational orientation of the therapydelivery member relative to the base based on a position of the markerrelative to the base.
 27. The method of claim 26, wherein determiningthe rotational orientation of the therapy delivery member relative tothe base based on a position of the marker relative to the basecomprises generating a medical image of the patient to locate themarker,
 28. A system comprising: means for covering a burr hole in acranium of a patient, wherein the means for covering the burr holedefines an opening configured to receive a therapy delivery member; andmeans for indicating a rotational orientation of the therapy deliverymember relative to the means for covering the burr hole.
 29. The systemof claim 28, wherein the means for indicating a rotational orientationof the therapy delivery member relative to the means for covering theburr hole comprises an reactive element, wherein a characteristic of thereactive element changes based on a rotational position of a firstmarker of the means for covering the burr hole, wherein the first markeris configured to be substantially aligned with a second marker of thetherapy delivery member.
 30. The system of claim 28, wherein the meansfor indicating the rotational orientation of the therapy delivery memberrelative to the means for covering the burr hole is visible and at leastpartially radiopaque.
 31. A method comprising: determining acharacteristic of a reactive element that changes based on a rotationalposition of a marker of a burr hole cap assembly relative to a base ofthe burr hole cap assembly, wherein the base is configured to fit insideof a burr hole in a cranium of a patient and defines an opening that isconfigured to receive a therapy delivery member; and with a processor,determining a rotational orientation of the therapy delivery memberrelative to the base based on a parameter indicative of thecharacteristic of the reactive element.
 32. The method of claim 31,wherein the reactive element comprises an inductor and thecharacteristic comprises a parameter indicative of at least one of aninductance or an inductive reactance of the inductor.
 33. The method ofclaim 31, wherein the reactive element comprises a capacitive elementand the characteristic comprises a capacitance of the capacitiveelement.